Disable double click based on mouse position

In the MouseDown event of a flexgrid I can access the y co-ordinate of the mouse.

When you double click on a flexgrid - I assume the mouse down event triggers first.

When I right click on a particular flexgrid I pop up a menu.
when I double click on the flexgrid, I show a form.

If I click on the flexgrid below the last row, I don't want the double click to work.

So, how can I detect the y position of the mouse when I double click?
If I retrieve it from the mouse down event - and determine the mouse has been clicked below the last row of the grid - how can I cancel the double click event?

i.e. if in the first click of a double click I determine I want to cancel the double click, how can I do that?

Thanks for any help.