twitter_URL_Regex.php

$testUsername = "https://twitter.com/webdevronsocial";
$regEx = '/(?:https?:\/\/)?(?:www\.)?twitter\.com\/(?:#!\/)?@?([a-zA-Z0-9_]{1,15})/';

if( preg_match( $regEx, $testUsername, $matches ) ){
    /**
     This is valid, play your code here
     - $matches[0] will returns the profile URl
     - $matches[1] will returns the Username
    */
}