new column added in dataSet designer not appearing in DisplayMember

(Learning VB)
In DataSet Designer I had a DataSet of EmplyeeID , firstName and lastName and added a column FullName to concatenate the first and last names.

Now FullName is listed in Data Sources and works on a form on its own. The trouble is, when I try to bind it to a different ComboBox, it doesn't show up in the Display Member drop box with the rest of the DataSet.

Any thoughts would be helpful