Billy Moon is the brother of Daphne Moon on the sitcom Frasier. He appears only briefly at Donny and Daphne's wedding. He is the son of Gertrude and Harry Moon. He is a ballroom dancer, and is Daphne's favorite brother, along with Stephen Moon. He is also gay, and acknowledged as such by all the family.
He has never peeked in on Daphne while she was undressing or showering, as all the others did during their years of pubescence. He did peek on all the other brothers though.
Although mentioned on a few occasions, he is never clearly seen and identified onscreen.