ASP.NET confirmation box showing twice

[rokgodiaday]

I've searched for a way to display a confirmation box when a certain button is pressed.The only problem I have, is that the confirmation box shows twice.Code:\[code\]<dx:ASPxButton ID="btnDel" runat="server" onClick="btnDel_Click" Text="Delete">\[/code\]and in Page_Load:\[code\]btnDel.Attributes.Add("onclick", "return confirm('Are you sure?');");\[/code\]