Checkbox in unbound datagridview (windows app)

Question

I'm trying to find an event that fires when the checkbox within an unbound datagridview is changed.

I've tried several and the closest I can find so far is on CellValidating but that does not fire until they actually level the cell.

CellContectClick (and several variations) all fire before the checkbox is changed so that is not ideal but it could also be used if there are no better options.