We asked if his personal relationship with the disgraced Clippers owner -- which spanned more than 2 decades -- made it even harder to dish out the punishment. Silver's answer seems pretty genuine.
NBA Commissioner Adam Silver tells us ... making the decision to ban Donald Sterling from the league for life was "very difficult" ... but it's business -- and it had to be done.
Silver was out in NYC yesterday when he began talking to TMZ Sports -- which he says has consistently shocked him.
But at the end of the day, Silver says ... "It's business. And I think he understood that as well."
Bonus -- Silver says he's a huge Justin Bieber fan ... but then he kinda disses Austin Mahone.
The Mahomies are gonna be pisssssed!!!!!!