Complex sentence: Robey travelled to Birmingham in 1906 where he played the title role in "Queen of Hearts", a pantomime which Cotes describes as "the most famous of all famous Birmingham Theatre Royal pantomimes".
Split into simpler sentences: Robey travelled to Birmingham in 1906 where he formed part of the cast of the pantomime "Queen of Hearts". He took the part of Queen in what Cotes describes as "the most famous of all famous Birmingham Theatre Royal pantomimes".