Clear bootstrap modal on browser back button click in ASP.Net

Hi DARKFOXX,

Refer below code.

HTML

<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"
    integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js"
    integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css"
    integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js"
    integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>
<center>
        <asp:Button ID="btnShowPopup" runat="server" Text="Show Popup" OnClick="ShowPopup" CssClass="btn btn-info btn-lg" />
</center>
<div id="MyPopup" class="modal fade" role="dialog">
    <div class="modal-dialog">
        <div class="modal-content">
            <div class="modal-header">
                <h4 class="modal-title">Greetings</h4>
                <button type="button" class="close" data-dismiss="modal">&times;</button>
            </div>
            <div class="modal-body">
                Welcome to ASPSnippets.com
            </div>
            <div class="modal-footer">
                <button type="button" class="btn btn-danger" data-dismiss="modal">Close</button>
            </div>
        </div>
    </div>
</div>
<script type="text/javascript">
    function ShowPopup() {
        $("#MyPopup").modal("show");
    }
    $(function () {
        $(window).on('popstate', function () {
            $('#MyPopup').modal('hide');
            $(".modal-backdrop").remove();
            $(".in").remove();
        });
    });
</script>

Code

C#

protected void ShowPopup(object sender, EventArgs e)
{
    ScriptManager.RegisterStartupScript(this, this.GetType(), "Popup", "ShowPopup();", true);
}

VB.Net

Protected Sub ShowPopup(ByVal sender As Object, ByVal e As EventArgs)
    ScriptManager.RegisterStartupScript(Me, Me.GetType(), "Popup", "ShowPopup();", True)
End Sub