Joey Bosa's Brother: Our Grandpa's a Mob Legend ... But I Can't Talk About It

Ain't no Sammy "The Bull" Gravanos in the Bosa family -- 'cause the brother of NFL rookie Joey Bosa says he ain't about to snitch on his famous great-grandpa ... who's a Chicago mob LEGEND.

Joey was just drafted #3 to the San Diego Chargers ... but we spoke with his lil' bro Nick (who's playing for Ohio State next season) and asked about Tony Accardo ... the Bosa's great-grandpa.

Accardo was an uber famous mafioso ... first serving as Al Capone's underboss, then eventually rising to all-out boss of the Chicago Outfit in the 1940's.

Seriously, click here to read all about the guy.

So, when we asked Nick to share any stories about Tony ... he gave a response his great-grandfather would definitely love.

"That's not something I should really be talking about."