$string = "Ajay Devgn Vijay Salgaonkar Shriya Saran Nandini Salgaonkar Tabu Meera Deshmukh Rajat Kapoor Mahesh Deshmukh Ishita Dutta Anju Salgaonkar Prasanna Ketkar Sr. PI Shrikant Prabhu Prathamesh Parab";
$a = preg_replace('/(\S+\s+\S+)\s/', '$1,', $string);
echo $a."<hr>";
$b = explode(",",$a);
shuffle($b);
echo implode(",",$b);