Max - brother of Thom - has been signed until the end of the season and said in The Scotsman: "I am hugely excited at the prospect of being more involved in the professional game, especially alongside Thom.
"He has made a tremendous impression in his first season at Hughenden and I would love to follow in his footsteps.
"Although we have played together in sevens, the last time we teamed up in a full game was away back when we were schoolboys at Wellington College.
"After that I went to Harlequins, and Thom went through his much-publicised boy-band spell before going to Wasps, so there was no opportunity to appear together."