Last night (April 8) at the Forum in Los Angeles, Justin Bieber was a surprise guest during Ariana Grande's set. The duo performed "As Long As You Love Me" to raucous cheers from the audience. But it was body language, not the music, that was making headlines last night and into this morning. As video obtained by TMZ shows, during the song, Bieber creeped up behind Grande, clasping his hands around her waist. Evidently uncomfortable, Grande moved away and continued the performance, although nothing seemed to fully curb the Canadian pop star's handsy behavior.

This did little to please Grande's boyfriend, Big Sean. The Detroit rapper wasn't in attendance, but once he caught wind of the performance, he reportedly tweeted two messages that have since been deleted. The first read simply, "Wow," while the second was more pointed: "This kid is about to learn not to touch my girl like that. Beliebe that."

Sean has had a banner year professionally; his third album, Dark Sky Paradise, debuted atop the Billboard charts and featured contributions from the likes of Drake and Kanye West. His relationship with Grande has been public for some time now, making them one of the highest-selling couples in contemporary pop music. As for Bieber, he recently attempted to stage a public rebranding of sorts with a roast on Comedy Central, in which he apologized to his fans and the public at large for some of his conduct over the past few years. His last full-length project, the 2013 compilation Journals, actually featured Sean on the song "Memphis," which also sported a guest spot from Diplo. Sean's biggest hit to date, "IDFWU," is over a DJ Mustard beat that was initially given to Bieber.

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