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They almost fought in line at a Vegas buffet in 2019 -- but UFC star Colby Covington and fighter manager Ali Abdelaziz have buried the hatchet in 2020 ... with a little help from Donald Trump.

First, some backstory!!!

Ali represents some of the biggest names in MMA -- from Khabib to Justin Gaethje, Kamaru Usman, Henry Cejudo and more.

Back in early 2019, Colby was trying to set up a welterweight title fight with Kamaru ... and the trash talk got so personal, things came to a head at the buffet at The Palms in Vegas.

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Colby was in line ... and Ali gets in his face -- and Kamaru had to hold Abdelaziz back! Intense!!!

So, what happened since?

Ali -- along with Henry Cejudo and Justin Gaethje -- were invited to hang with Trump at his rally in Nevada on Sunday ... where Covington was also a VIP guest of the President.

Ali tells us ... since the two men were forced to hang out, they made the best of the situation and talked things out. And, as of now, they're cool.

"I don't hate the kid, I don't have no ill will towards him. He was there to represent the President, I was there to represent the President. If he fought Kamaru or Gilbert or any of my guys again, he becomes the enemy again, it's simple."

"But, right now he's not the enemy. He's a guy trying to make a name for himself."

As for meeting Trump, Ali says it was one of the highlights of his life -- and says Trump treated him like one of the boys!

There's more ... Ali also talked about the upcoming matchup between Kahbib and Gaethje (both are his clients) and explained why it could be one of the greatest fights in MMA history!