How to open an iframe in a modal a wordpress template

This code makes me open an iframe in a modal:

<a data-toggle="modal" data-target="#myModal">
  OPEN MODAL
</a>

<div class="modal fade" id="myModal" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
  <div class="modal-dialog" style="width: 80%">
    <div class="modal-content">

      <div class="modal-body">
          <iframe src="https://getbootstrap.com/getting-started/" width="100%" height="580" frameborder="0" allowtransparency="true"></iframe>
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
      </div>
    </div>
  </div>
</div>

I’m modify this wordpress template. In section “Portfolio”, clicking on the icon in the photo, it opens another page. I want to make this page to open inside the iframe.

ORIGINAL CODE

$foutput.='
<div class="mega-hover">
<a target="_blank" href="'.$page_url.'">
   <div class="mega-hoverlink"><i class="fa fa-link"></i></div>
</a>';

MY CODE:

$foutput.='
<div class="mega-hover">

<!-- MY MODAL ADD IN LINK -->
<a data-toggle="modal" data-target="#MYMODAL">
 <div class="mega-hoverlink"><i class="fa fa-link"></i></div>
</a>';

The above code calls the modal.

This is the modal code:

<div class="modal fade" id="MYMODAL" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
 <div class="modal-dialog" style="width: 80%">
   <div class="modal-content">
      <div class="modal-body">
       <iframe src="'.$page_url.'" width="100%" height="100%" frameborder="0" allowtransparency="true"></iframe>
       </div>
      <div class="modal-footer">
            <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
       </div>
     </div>
  </div>
</div>

The problem is that the modal does not find the page ‘.$page_url.’. As I reviewed the code, the variable $foutput stores all information as mounting html / structure of divs, buttons, links, etc.

I tried to create a variable with the modal code, and end of code I put a return, but but without success.

How can I do this?
How do I open the iframe ‘.$page_url.’