Play video content Exclusive TMZSports.com

Colby Covington's support for President Trump has turned into an all-out bromance with POTUS' son ... 'cause Donald Trump Jr. says he considers the UFC star a good friend!!

Of course, the Trump family has been frequenting UFC events lately -- Trump Jr. and Eric were Covington's personal guests to his fight against Robbie Lawler in Aug. ... and they both attended UFC 244 last weekend with #45 himself.

As for Colby, he's been invited to 1600 Penn ... and even snapped a pic with Trump in the Oval Office.

So, when we saw DTJ out in NYC on Tuesday, we had to ask about the UFC megafight -- and if he'd ever consider walking a fighter out to the Octagon.

"I'd go out with Colby," Trump Jr. told us ... "He's become a good friend. There's a lot of great fighters out there but Colby's become a friend."

He might get his wish soon ... Colby is set to fight Kamaru Usman for the UFC welterweight championship at UFC 245 on Dec. 14 at the T-Mobile Arena in Vegas.