Adding a line to a Gridview that is databinded, C#

I have a GridView that displays the results from a Query that is Databound.
How can I manually add a new line or row after the Query does its databind, so that it will display in the GridView.
e.g. One of the column names is "FirstName", I'd like to add a new row in the "FirstName" column with a value of "Test".
Thank you !
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