Insert "@" character in a php code

Hi, I have a board in phpbb and I want to make a little modification in php code.

This is the original code:

$message_parser->message = '[quote="' . $post_data['quote_username'] . '[url=' . generate_board_url() . "/viewtopic.$phpEx?p=$post_id#p$post_id" . ']' . ' » ' . date("jS F Y, G:i:s", $post_data['post_time']) . '[/url]' . '"]' . censor_text(trim($message_parser->message)) . "[/quote]\n"; 

I want to insert a "@" character before the name of the quoted user: $post_data['quote_username']

It needs to be attached to the username (no spaces between the "@" and the username).

I know that is a strange request but I would be extremely grateful to who will help me with this snippet.