Complex sentence: Avis later joined English National Ballet as First Soloist in 2002, before returning to the Royal Ballet in 2004, where he was promoted to Principal Character Artist in 2005, and Assistant Ballet Master in 2007.
Split into simpler sentences: Avis later joined English National Ballet as First Soloist in 2002, returning to the Royal Ballet in 2004. He was promoted to Principal Character Artist in 2005 and Assistant Ballet Master in 2007.