Index: post.php
===================================================================
--- post.php	(revision 18378)
+++ post.php	(working copy)
@@ -5190,6 +5190,25 @@
 }
 
 /**
+ * Removes a post thumbnail.
+ *
+ * @param int|object $post Post ID or object where thumbnail should be removed from.
+ * @return bool True on success, false on failure.
+ */
+function delete_post_thumbnail( $post ) {
+	$post = get_post( $post );
+	if ( $post ) {
+		$thumbnail_id = get_post_meta( $post->ID, '_thumbnail_id', true );
+		if ( ! empty( $thumbnail_id ) ) {
+			delete_post_meta( $post->ID, '_thumbnail_id' );
+			return true;
+		}
+		return true;
+	}
+	return false;
+}
+
+/**
  * Returns a link to a post format index.
  *
  * @since 3.1.0