C# WPF: FrameworkElementFactory add ComboBox Event Handler for DropDownClosed

Question

I'm struggling to add the event "DropDownClosed" to my ComboBox template similar to how you can do for other events like:

ComboBox_Template.AddHandler(GotFocusEvent, new RoutedEventHandler(ComboBox_GotFocus));

I tried to add it by simply writing

Cmb_Template.AddHandler(ComboBox.DropDownClosed, new EventHandler<RoutedEventArgs>(cmb_OtdCategory_DropDownClosed));

but ComboBox.DropDownClosed just doesn't exist.