Board Thread:General Discussion/@comment-5977816-20140220201837/@comment-74.192.154.45-20180227222516

On Netflix, in the shows description it says "This family-oriented retelling of the King Arthur legend finds Merlin arriving in Camelot, where he hones his magic skills with the help of his uncle", and Gaius is the one who helps Merlin hone his magic skills, so yes, I believe Gaius is Merlin's uncle.