The MTV Artists to Watch show at Los Angeles' House of Blues hosted a night of diverse acts, all framed by a sea of cellphones.

The expected roster brought the energy: Rixton, Echosmith, Tori Kelly, Jake Miller and Fifth Harmony. What the audience didn't know was that Ariana Grande would be surprising them during Tori Kelly's already memorable set. As Kelly was covering Grande's "Right There," Grande hopped onstage to join. Fans clutched to their phones to take pictures and video, which could hardly be heard amid the screaming.

We grabbed a pixelated video of our own for The Music Times Instagram, but luckily RoshonaWoods posted a high-quality YouTube video you can watch below.

To set up the cover, Kelly explained she's been messing around with the song a lot lately and really likes it. She said: "I'm a huge fan of this person. She's become a really good friend of mine. And we're super chill..."

The show was live-streamed to fans across the web. In other words, twitter exploded with other highlights from the night.

The evening kicked off with UK's boy band Rixton, who performed their hit "Make Out" to a chanting audience. Rixton made reference to their video parodying music's biggest pop stars. Next up was Echosmith, the "alt-pop quartet" from Los Angeles. They maintained the momentum, making the crowd sing and clap along to "Cool Kids."

Jake Miller opened with "Collide" and kept everyone dancing, despite being the second last act of the evening. Miller ended with a slightly toned-down "A Million Lives," accompanied by acoustic.

Fifth Harmony closed out the night with coordinated dance moves and charisma that kept the crowd packed. The X Factor stars' singing gave a serious nod to the 90s. The vibe of the show altogether was brimming with positivity -- the young audience was engaged until the end.

Watch Ariana Grande and Tori Kelly's duet here:

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