diff --git a/src/wp-includes/post.php b/src/wp-includes/post.php
index 67b14b8e35052..f8ac023cdfdf0 100644
--- a/src/wp-includes/post.php
+++ b/src/wp-includes/post.php
@@ -6869,6 +6869,33 @@ function wp_delete_attachment_files( $post_id, $meta, $backup_sizes, $file ) {
 		}
 	}
 
+	/*
+	 * Delete the animated-GIF video companions. When the client-side media flow
+	 * converts an opaque animated GIF to a web-safe video, the converted MP4/WebM
+	 * and a static first-frame JPEG poster are sideloaded alongside the GIF and
+	 * recorded under the 'animated_video' and 'animated_video_poster' keys. These
+	 * are kept separate from 'original_image', which continues to point at the GIF.
+	 */
+	foreach ( array( 'animated_video', 'animated_video_poster' ) as $companion_key ) {
+		if ( empty( $meta[ $companion_key ] ) || ! is_string( $meta[ $companion_key ] ) ) {
+			continue;
+		}
+
+		if ( empty( $intermediate_dir ) ) {
+			$intermediate_dir = path_join( $uploadpath['basedir'], dirname( $file ) );
+		}
+
+		$companion_file = str_replace( wp_basename( $file ), $meta[ $companion_key ], $file );
+
+		if ( ! empty( $companion_file ) ) {
+			$companion_file = path_join( $uploadpath['basedir'], $companion_file );
+
+			if ( ! wp_delete_file_from_directory( $companion_file, $intermediate_dir ) ) {
+				$deleted = false;
+			}
+		}
+	}
+
 	if ( is_array( $backup_sizes ) ) {
 		$del_dir = path_join( $uploadpath['basedir'], dirname( $meta['file'] ) );
 
diff --git a/src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php b/src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
index e0ee88052a9c2..41743d1717509 100644
--- a/src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
+++ b/src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
@@ -123,6 +123,9 @@ public function register_routes() {
 									$valid_sizes[] = 'full';
 									// Source-format original (e.g. the HEIC kept alongside its JPEG derivative).
 									$valid_sizes[] = self::IMAGE_SIZE_SOURCE_ORIGINAL;
+									// Converted-video companions for an animated GIF (the MP4/WebM and its poster).
+									$valid_sizes[] = 'animated_video';
+									$valid_sizes[] = 'animated_video_poster';
 
 									$items = is_string( $value ) ? array( $value ) : ( is_array( $value ) ? $value : null );
 									if ( null === $items ) {
@@ -2225,6 +2228,13 @@ public function sideload_item( WP_REST_Request $request ) {
 			 * under the dedicated source-image meta key.
 			 */
 			$sub_size_data['file'] = wp_basename( $path );
+		} elseif ( 'animated_video' === $image_size || 'animated_video_poster' === $image_size ) {
+			/*
+			 * Converted-video companion of an animated GIF (the MP4/WebM or
+			 * its static first-frame poster). Record the filename so
+			 * finalize_item can store it under its dedicated meta key.
+			 */
+			$sub_size_data['file'] = wp_basename( $path );
 		} elseif ( 'scaled' === $image_size ) {
 			// Record the current attached file as the original.
 			$current_file = get_attached_file( $attachment_id, true );
@@ -2389,6 +2399,16 @@ public function finalize_item( WP_REST_Request $request ) {
 				 * is handled by wp_delete_attachment_files().
 				 */
 				$metadata[ self::META_KEY_SOURCE_IMAGE ] = $sub_size['file'];
+			} elseif ( 'animated_video' === $image_size ) {
+				/*
+				 * Converted-video companion of an animated GIF. Stored under its
+				 * own meta key; 'original_image' keeps pointing at the GIF. Cleanup
+				 * on attachment delete is handled by wp_delete_attachment_files().
+				 */
+				$metadata['animated_video'] = $sub_size['file'];
+			} elseif ( 'animated_video_poster' === $image_size ) {
+				// Static first-frame poster for the converted video.
+				$metadata['animated_video_poster'] = $sub_size['file'];
 			} elseif ( 'scaled' === $image_size ) {
 				if ( ! empty( $sub_size['original_image'] ) ) {
 					$metadata['original_image'] = $sub_size['original_image'];
diff --git a/tests/phpunit/tests/media/wpDeleteAttachmentAnimatedGifVideo.php b/tests/phpunit/tests/media/wpDeleteAttachmentAnimatedGifVideo.php
new file mode 100644
index 0000000000000..9d0f8eddb446b
--- /dev/null
+++ b/tests/phpunit/tests/media/wpDeleteAttachmentAnimatedGifVideo.php
@@ -0,0 +1,129 @@
+<?php
+
+/**
+ * Tests that wp_delete_attachment_files() removes the animated-GIF video companions.
+ *
+ * @group media
+ * @covers ::wp_delete_attachment_files
+ */
+class Tests_Media_wpDeleteAttachmentAnimatedGifVideo extends WP_UnitTestCase {
+
+	public function tear_down(): void {
+		$this->remove_added_uploads();
+
+		parent::tear_down();
+	}
+
+	/**
+	 * @ticket 65549
+	 */
+	public function test_deletes_video_and_poster_companions(): void {
+		$attachment_id = self::factory()->attachment->create_upload_object( DIR_TESTDATA . '/images/canola.jpg' );
+		$this->assertIsInt( $attachment_id );
+
+		$attached_file = get_attached_file( $attachment_id, true );
+		$this->assertIsString( $attached_file );
+		$dir         = dirname( $attached_file );
+		$video_name  = 'companion-' . wp_generate_password( 6, false ) . '.mp4';
+		$poster_name = 'companion-' . wp_generate_password( 6, false ) . '.jpg';
+		$video_path  = $dir . '/' . $video_name;
+		$poster_path = $dir . '/' . $poster_name;
+
+		// Create dummy companion files on disk.
+		file_put_contents( $video_path, 'test' );
+		file_put_contents( $poster_path, 'test' );
+		$this->assertFileExists( $video_path, 'Video fixture should be on disk.' );
+		$this->assertFileExists( $poster_path, 'Poster fixture should be on disk.' );
+
+		// Record the companions as the sideload route does.
+		$metadata = wp_get_attachment_metadata( $attachment_id, true );
+		$this->assertIsArray( $metadata );
+		$metadata['animated_video']        = $video_name;
+		$metadata['animated_video_poster'] = $poster_name;
+		wp_update_attachment_metadata( $attachment_id, $metadata );
+
+		wp_delete_attachment( $attachment_id, true );
+
+		$this->assertNull( get_post( $attachment_id ) );
+		$this->assertFileDoesNotExist( $video_path, 'Video companion should be deleted alongside the attachment.' );
+		$this->assertFileDoesNotExist( $poster_path, 'Poster companion should be deleted alongside the attachment.' );
+	}
+
+	/**
+	 * @ticket 65549
+	 */
+	public function test_deletes_only_video_when_no_poster_recorded(): void {
+		$attachment_id = self::factory()->attachment->create_upload_object( DIR_TESTDATA . '/images/canola.jpg' );
+		$this->assertIsInt( $attachment_id );
+
+		$attached_file = get_attached_file( $attachment_id, true );
+		$this->assertIsString( $attached_file );
+		$dir        = dirname( $attached_file );
+		$video_name = 'companion-' . wp_generate_password( 6, false ) . '.mp4';
+		$video_path = $dir . '/' . $video_name;
+
+		file_put_contents( $video_path, 'test' );
+		$this->assertFileExists( $video_path, 'Video fixture should be on disk.' );
+
+		$metadata = wp_get_attachment_metadata( $attachment_id, true );
+		$this->assertIsArray( $metadata );
+		$metadata['animated_video'] = $video_name;
+		wp_update_attachment_metadata( $attachment_id, $metadata );
+
+		wp_delete_attachment( $attachment_id, true );
+
+		$this->assertNull( get_post( $attachment_id ) );
+		$this->assertFileDoesNotExist( $video_path, 'Video companion should be deleted alongside the attachment.' );
+	}
+
+	/**
+	 * @ticket 65549
+	 */
+	public function test_noop_when_no_companion_metadata(): void {
+		$attachment_id = self::factory()->attachment->create_upload_object( DIR_TESTDATA . '/images/canola.jpg' );
+		$this->assertIsInt( $attachment_id );
+
+		// Sanity: no companion keys on freshly-created metadata.
+		$metadata = wp_get_attachment_metadata( $attachment_id, true );
+		$this->assertIsArray( $metadata );
+		$this->assertArrayNotHasKey( 'animated_video', $metadata );
+		$this->assertArrayNotHasKey( 'animated_video_poster', $metadata );
+
+		// Deletion should complete cleanly even though no companion file is recorded.
+		wp_delete_attachment( $attachment_id, true );
+
+		$this->assertNull( get_post( $attachment_id ) );
+	}
+
+	/**
+	 * Guards against a companion key holding a non-string value (e.g. the array
+	 * form some metadata flows write).
+	 *
+	 * @ticket 65549
+	 */
+	public function test_noop_when_companion_metadata_is_not_a_string(): void {
+		$attachment_id = self::factory()->attachment->create_upload_object( DIR_TESTDATA . '/images/canola.jpg' );
+		$this->assertIsInt( $attachment_id );
+		$attached_file = get_attached_file( $attachment_id, true );
+		$this->assertIsString( $attached_file );
+
+		/*
+		 * Place a real file that a buggy, guard-less implementation could try to
+		 * delete after running wp_basename() over the array value below.
+		 */
+		$bystander_path = dirname( $attached_file ) . '/should-not-delete.mp4';
+		file_put_contents( $bystander_path, 'test' );
+		$this->assertFileExists( $bystander_path, 'Test fixture should be on disk.' );
+
+		$metadata = wp_get_attachment_metadata( $attachment_id, true );
+		$this->assertIsArray( $metadata );
+		$metadata['animated_video'] = array( 'file' => 'should-not-delete.mp4' );
+		wp_update_attachment_metadata( $attachment_id, $metadata );
+
+		// Deletion should not raise (no str_replace() / file deletion on an array).
+		wp_delete_attachment( $attachment_id, true );
+
+		$this->assertNull( get_post( $attachment_id ) );
+		$this->assertFileExists( $bystander_path, 'The non-string guard must prevent any file deletion.' );
+	}
+}
diff --git a/tests/phpunit/tests/rest-api/rest-attachments-controller.php b/tests/phpunit/tests/rest-api/rest-attachments-controller.php
index 43ad46881ca09..3c697be4cedb0 100644
--- a/tests/phpunit/tests/rest-api/rest-attachments-controller.php
+++ b/tests/phpunit/tests/rest-api/rest-attachments-controller.php
@@ -3574,6 +3574,77 @@ public function test_sideload_source_original_writes_metadata_source_image(): vo
 		$this->assertArrayNotHasKey( 'original_image', $metadata, "Metadata 'original_image' should be untouched by the HEIC sideload." );
 	}
 
+	/**
+	 * Tests sideloading the animated-GIF video companions ('animated_video' and
+	 * 'animated_video_poster'). Each filename is recorded under its own metadata
+	 * key by the finalize endpoint and does not collide with 'original_image',
+	 * which keeps pointing at the GIF.
+	 *
+	 * The uploaded bytes are a JPEG stand-in: the sideload branch only records
+	 * wp_basename() of the stored file, so the metadata plumbing can be exercised
+	 * without depending on video upload support in the test environment.
+	 *
+	 * @ticket 65549
+	 * @requires function imagejpeg
+	 */
+	public function test_sideload_animated_video_companions_write_metadata(): void {
+		$this->enable_client_side_media_processing();
+
+		wp_set_current_user( self::$author_id );
+
+		// Create the (GIF) attachment the companions belong to.
+		$request = new WP_REST_Request( 'POST', '/wp/v2/media' );
+		$request->set_header( 'Content-Type', 'image/jpeg' );
+		$request->set_header( 'Content-Disposition', 'attachment; filename=canola.jpg' );
+		$request->set_body( (string) file_get_contents( self::$test_file ) );
+		$response      = rest_get_server()->dispatch( $request );
+		$attachment_id = $response->get_data()['id'];
+		$this->assertSame( 201, $response->get_status() );
+
+		// Sideload the converted-video companion.
+		$request = new WP_REST_Request( 'POST', "/wp/v2/media/{$attachment_id}/sideload" );
+		$request->set_header( 'Content-Type', 'image/jpeg' );
+		$request->set_header( 'Content-Disposition', 'attachment; filename=canola-video.jpg' );
+		$request->set_param( 'image_size', 'animated_video' );
+		$request->set_body( (string) file_get_contents( self::$test_file ) );
+		$video_response = rest_get_server()->dispatch( $request );
+		$this->assertSame( 200, $video_response->get_status(), 'Sideloading animated_video should succeed.' );
+		$video_sub_size = $video_response->get_data();
+		$this->assertIsArray( $video_sub_size );
+		$this->assertSame( 'animated_video', $video_sub_size['image_size'], 'Response should echo the image_size.' );
+
+		// Sideload the poster companion.
+		$request = new WP_REST_Request( 'POST', "/wp/v2/media/{$attachment_id}/sideload" );
+		$request->set_header( 'Content-Type', 'image/jpeg' );
+		$request->set_header( 'Content-Disposition', 'attachment; filename=canola-poster.jpg' );
+		$request->set_param( 'image_size', 'animated_video_poster' );
+		$request->set_body( (string) file_get_contents( self::$test_file ) );
+		$poster_response = rest_get_server()->dispatch( $request );
+		$this->assertSame( 200, $poster_response->get_status(), 'Sideloading animated_video_poster should succeed.' );
+		$poster_sub_size = $poster_response->get_data();
+		$this->assertIsArray( $poster_sub_size );
+		$this->assertSame( 'animated_video_poster', $poster_sub_size['image_size'], 'Response should echo the image_size.' );
+
+		// Sideload must not write metadata; that happens in finalize.
+		$metadata = wp_get_attachment_metadata( $attachment_id, true );
+		$this->assertArrayNotHasKey( 'animated_video', $metadata, 'Sideload should not write animated_video metadata.' );
+		$this->assertArrayNotHasKey( 'animated_video_poster', $metadata, 'Sideload should not write animated_video_poster metadata.' );
+
+		// Finalize with both collected sub-sizes, which writes the metadata.
+		$request = new WP_REST_Request( 'POST', "/wp/v2/media/{$attachment_id}/finalize" );
+		$request->set_param( 'sub_sizes', array( $video_sub_size, $poster_sub_size ) );
+		$response = rest_get_server()->dispatch( $request );
+		$this->assertSame( 200, $response->get_status(), 'Finalize should succeed.' );
+
+		$metadata = wp_get_attachment_metadata( $attachment_id );
+		$this->assertIsArray( $metadata );
+		$this->assertArrayHasKey( 'animated_video', $metadata, "Metadata should contain 'animated_video'." );
+		$this->assertMatchesRegularExpression( '/canola-video.*\.jpg$/', $metadata['animated_video'], "Metadata 'animated_video' should reference the video companion filename." );
+		$this->assertArrayHasKey( 'animated_video_poster', $metadata, "Metadata should contain 'animated_video_poster'." );
+		$this->assertMatchesRegularExpression( '/canola-poster.*\.jpg$/', $metadata['animated_video_poster'], "Metadata 'animated_video_poster' should reference the poster filename." );
+		$this->assertArrayNotHasKey( 'original_image', $metadata, "Metadata 'original_image' should be untouched by the companion sideloads." );
+	}
+
 	/**
 	 * Tests the filter_wp_unique_filename method handles the -scaled suffix.
 	 *