Nyjah Huston Teases 'Special' Machine Gun Kelly Appearance at Santa Monica SLS Event

Those taking the PCH to catch Friday's SLS better be prepared for Machine Gun Kelly -- Nyjah Huston tells TMZ Sports he's expecting MGK to roll through the Street League Skateboarding event!!

The competition officially kicks off at the Santa Monica Pier in just a few hours -- at 1:30 PM PT, to be exact -- and while most fans will come to watch Huston and other skaters throw down tricks ... the Olympic bronze medalist told us MGK is gonna get in on the fun, too.

Huston was super careful about what the "my ex's best friend" crooner will do at the event ... but said it'll be "special."

"I'm not going to give it away," the star skater added, "but it sounds super sick."

The entire event looks like it'll be must-see, as Huston called the location a straight up "legendary skate spot."

Plus, he told us he can't wait to flip his board by the Pacific Ocean -- considering as a California-native, it's basically his backyard.

"It's going to be a great vibe," Huston told us. "I love that it's a free event -- just invite all the fans to come out and have a good time."