Details on who Barrowman will play are not currently clear, and Rhimes later added: "Here's the deal: I'm trying not to give away ANY spoilers -- my GA fans are FAB at gleaning info from tweets! #lipszipped"
According to The Hollywood Reporter, his scenes will air in the penultimate episode of the season on May 9.
Barrowman and Rhimes worked together on period drama pilot Gilded Lilys last year, but it was not picked up to series.
Rhimes previously joked that she would be "stalking [Barrowman] until the end of time".
Sources:
Digital Spy
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