System.Object
   System.EventArgs
      C1.WPF.FlexGrid.PropertyGroupCreatedEventArgs
   System.Windows.Threading.DispatcherObject
      System.Windows.DependencyObject
         System.Windows.Media.Visual
            System.Windows.UIElement
               System.Windows.FrameworkElement
                  System.Windows.Controls.Control
                     C1.WPF.FlexGrid.C1FlexGridGroupPanel

Reference

C1.WPF.FlexGrid.GroupPanel.4 Assembly