Conor McGregor Arrives in Style to After-Party to Celebrate Victory.

Conor McGregor has twice the reason to party now -- 2 championship belts -- so you better believe he's gonna make the most of it.

We got the Irish UFC champ arriving at Marquee nightclub in NYC to celebrate his 2nd round KO against Eddie Alvarez ... making him the first fighter to hold 2 titles at the same time.

He showed up in his Notorious-mobile ... and got wild inside da club. Get it while you still can, Conor.