REGULAR EXPRESSION DATE VALIDATION in dd/mm/yyyy format

<asp:TextBox ID="txtDate" runat="server" ValidationGroup="ABC"></asp:TextBox>

                                                    <ajaxToolkit:CalendarExtender ID="CalDate" runat="server" TargetControlID="txtDate"

                                                        PopupButtonID="txtDate" Format="dd/MM/yyyy">

                                                    </ajaxToolkit:CalendarExtender>

                                                    <asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ErrorMessage="*"

                                                     ValidationExpression="^(?:(?:(?:0?[1-9]|1\d|2[0-8])\/(?:0?[1-9]|1[0-2]))\/(?:(?:1[6-9]|[2-9]\d)\d{2}))$|^(?:(?:(?:31\/0?[13578]|1[02])|(?:(?:29|30)\/(?:0?[1,3-9]|1[0-2])))\/(?:(?:1[6-9]|[2-9]\d)\d{2}))$|^(?:29\/0?2\/(?:(?:(?:1[6-9]|[2-9]\d)(?:0[48]|[2468][048]|[13579][26]))))$"

                                                    ControlToValidate="txtDate" Display="Dynamic" ValidationGroup="ABC"></asp:RegularExpressionValidator>