adding cobo box to datagridview

I populate a datagridview with the query:

Select Col1, Col2, Col3, Col4, Reason from tbla

I want to add a combox box where the reason is.  The value of the Reason is a code 3digits
Example "048"  I want to look up the description for that code and display the description in the cobo box.  If the were were updated, I want the code not the description.

The query to get the code Select DESC from Desc_tble wher Reason = '048'

My question is how to create and set the properties to do this?