A Charli xcx and Lorde reunion, John Summit's homecoming and Sombr's collab with 5 Seconds of Summer led night one.
"love you ella, congrats on headlining and ty for bringing me out!!!!" the British star wrote.
Selena Gomez, Benny Blanco and Becky G have also unveiled their new summer single.
What do artists do at Lollapalooza when they're waiting around to go on, or they've already performed and decide to hang out?
"Saturday Night Live" alum Bobby Moynihan reveals he's a massive SNL nerd and couldn't help but geek out while working with ...
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