how to get most recent file from directory & sub-directories

[nupzee]

I have used the following script to correctly display the first file from the array across the selected directory and its sub-directories. Does anyone know how to modify this code to only echo the most recent file based on filemtime across the directory/subdirectories?

function ListFiles($dir) {

    if($dh = opendir($dir)) {

        $files = Array();
        $inner_files = Array();

        while($file = readdir($dh)) {
            if($file != "." && $file != ".." && $file[0] != '.') {
                if(is_dir($dir . "/" . $file)) {
                    $inner_files = ListFiles($dir . "/" . $file);
                    if(is_array($inner_files)) $files = array_merge($files, $inner_files); 
                } else {
                    array_push($files, $dir . "/" . $file);
                }
            }
        }

        closedir($dh);
        return $files;
    }
}

echo array_shift(ListFiles('media/media/images'));