PHP标题位置在Fancybox中打开

Currently I am using Fancybox for links in my page...

e.g.

<a class="fancybox fancybox.iframe more_info_btn"  href='<?=$someurl?>'>LINK1</a>

On my one page I have form , On submit user get redirected to another link . code used is as follows

<?php
.....
.....//all code
// and after that..
$url1 = 'http://example.com/page2.php';

$_SESSION["Register_id"]="suceess";
    header("Location: ".$url1); 
} 
?>

I needed help to redirect user with some changes in

header("Location: ".$url1);

to fancybox opened instead of page2.php in main browser tab ?