Removing a value from combobox

Question

I've two combo boxes listed with same values from the database.

If I select a value from the first combo box, that value should not be listed in the second combo box.

ComboBox1              ComboBox2 One                   One Two                   Two Three                 Three Four                   Four Five                   Five

If I select 'Three' from the ComboBox1, the value 'Three' should not be listed in ComboBox2 while making a selection from ComboBox2.