Bootstrap 4 How to open external url in modal dialog

<a href="#mymodal" data-remote="my-remote-file.php" data-toggle="modal" data-target="#mymodal">Launch demo modal</a>

<div class="modal" id="mymodal" tabindex="-1" role="dialog">
    <div class="modal-dialog modal-lg" role="document">
        <div class="modal-content">
            <div class="modal-header">
                <h5 class="modal-title">Modal title</h5>
                <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                    <span aria-hidden="true">&times;</span>
                </button>
            </div>
            <div class="modal-body">
                my-remote-file.php content
            </div>
            <div class="modal-footer">
                <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
                <button type="button" class="btn btn-primary">Save changes</button>
            </div>
        </div>
    </div>
</div>
<script>
$('#mymodal').on('show.bs.modal', function(e) {
    var button = $(e.relatedTarget);
    var modal = $(this);
    modal.find('.modal-body').load(button.data("remote"));
});
</script>