From the second paragraph of “Beach Boys in Coto concert,” a Saturday Orange County Register story by Mark Eades:
Before three of the original members – Mike Love, Bruce Johnston and John Stamos – took the stage, concert goers imbibed in a bit of food and drink at a pre-concert bash by the club's swimming pool.
The Beach Boys first formed in 1961. According to his bio, Stamos was not even born until 1963. Johnston also was not part of the original group, although he did join in the early days and was with the original, surviving members who were inducted into the Rock N Roll Hall of Fame in 1988.
Stamos and David Marks, who was also on stage with Johnston and the original members at the Hall of Fame induction, are often referred to as “honorary Beach Boys.”
Ironically, Al Jardine is often referred to as “an honorary Full House cast member.”