You will never guess who is set to guest star in the season finale of Moone Boy tonight, it's only bloody Paul Rudd! For reals. We have no idea who he is set to play as of yet, but we do know this episode is about Martin's grandad's imaginary friend, George Gershwin, who is a 'cool, piano-playing guy'. You know who likes to play piano? Paul Rudd. As we said, this is the last episode in the series, and there has been much speculation that it's the final ever, so take in as much of the Boyle antics as you can tonight, just in case.