The cat is out of the bag with the announcement Robbie Williams will star as the voice of Felix, the feline behind the Purina cat food brand, in a newly recorded song.The 48-year-old pop star sings "It’s Great To Be A Cat", a tune set to feature in new Felix adverts.Williams wrote and created the track, and will also appear in a short film premiering on Wednesday at 5pm. "This song is an absolute earworm," he says, promoting the track.