Getting the old selected index in Winform's Combo box

Seems like this is a possible duplicate

ComboBox SelectedIndexChanged event: how to get the previously selected index?

There is nothing built in, you will need to listen for this event and keep track in a class variable.

But this answer seems to suggest a sensible way of extending the combobox to keep track of the previous index https://stackoverflow.com/a/425323/81053