John Stamos -- I'm REUNITING with the Beach Boys!!!

John Stamos wasn't even born when the Beach Boys first got together ... but the actor tells TMZ ... he's been invited to play with the band on their upcoming 50th Anniversary Reunion tour.

Seems he was celebrating last night ... 'cause a boozy Stamos (but not boozy in a bad way) was hangin' at the Comedy Store on Sunset Blvd. when he revealed, "[The Beach Boys] asked me to be a part of the show ... I feel very honored."

The former "Full House" star performed with the band on a pretty regular basis during the '90s ... and participated in a few gigs in the past couple of years.

The band is reportedly set to kick things off at the Grammys next month ... followed by a 50-date tour.

So, how do good things keep happening to Stamos? Jesus loves the guy ... seriously, watch the clip.