Post Malone was in Detroit over the weekend, and decided to have a little fun with a band inside of the MGM Grand Casino.

Before his show on Sunday night, it appears Post Malone was taking in the sights and sounds of Detroit.

Collision Six was playing at the MGM Grand Casino in the Axis bar last Saturday (9/28). They got an unexpected surprise when Post Malone not only showed up, but asked to sit in with them.

Posty sang Sublime's "Santeria" with Collision Six, and thankfully, there was video.

By the looks of it, the Axis Bar in the MGM Grand Casino isn't all that big. So, to see someone of Post Malone's caliber in that small of a venue is something of a treat!

It made sense for him to do a Sublime song, as he was backed by Sublime with Rome earlier this year.

The keyboard player for the band, who posted the video, claimed that he wasn't really aware who Post Malone is, but that he was told that he's a "big deal."

Pretty sure he was joking. If not...yeah, bud. I'd say he's a pretty big deal.

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