Get parent page ID in WordPress

Legacy

function get_top_parent_page_id() {
	global $post;
	$ancestors = $post->ancestors;
	// Check if page is a child page (any level)
	if ($ancestors) {
	//  Grab the ID of top-level page from the tree
		return end($ancestors);
	} else {
		// Page is the top level, so use  it's own id
		return $post->ID;
	}
}

function get_top_parent_page_id() {

global $post;

$ancestors = $post->ancestors;

// Check if page is a child page (any level)

if ($ancestors) {

// Grab the ID of top-level page from the tree

return end($ancestors);

} else {

// Page is the top level, so use it's own id

return $post->ID;

}