Didn't Bieber train with Diaz bros at one point?
I don't know about trained, but Bieber had a bit to say on social media when Diaz beat Conor (I think Bieber and Conor met before and Bieber admired him):
Bieber wrote that Conor was “a true champion [that] fights with style and finesse" and called Diaz’s fighting style “terrible.”
Diaz told Rolling Stone: “Bieber don’t watch the sport; he don’t know the sport. I’ve seen a couple other people too, Drake, all these other guys that are stating their opinion. How are you going to state your opinion when you don’t know shit? You’re just showing your lack of knowledge on the sport,” he sad. “They picked McGregor. The mainstream got him because they know his name more, but if you look at my record and at look at who I am and watch my fights, you know [I was going to win]. Unless you’re caught up in the hype. Those guys all were.”
Anyway, Diaz and Bieber later squashed the beef: