Check out video of the pair bonding at the show!
The A-listers were chatting together in the VIP section at the O2 Arena when fans nearby began to take notice. Styles was dressed all in white, while the Stranger Things star rocked a black jacket over a white sweatshirt and black pants with a stripe up the leg.
"Harry? with Millie Bobby Brown? at Ariana Grande's concert? This just added 10 years to my life," one fan captioned a video of the celebs together. "Millie bobby brown and harry styles are at ariana grande's london show chatting together for the whole night...... the most ambitious crossover event in history," another wrote beside video of the stars' chance encounter.
"So you're telling me that harry styles and millie bobby brown were casually chatting at the ariana grande concert,,, a concert i was supposed to attend," another fan wrote of the meeting. "MY TWO WORLDS COLLIDED a b*tch is crying and that b*tch is me."
Later, the two were recorded dancing in the crowd, which naturally had fans in a frenzy.
"Everyone needs Harry Styles full on booty popping at an Ariana Grande show on their timeline," a fan commented. Another wrote: "Ariana grande was truly incredible but what topped my night was @Harry_Styles going ape sh*t dancing in the VIP."
There was some debate online as to whether the man dressed in white was in fact 25-year-old Styles. But, a clip showing the crooner greeting fans while leaving the venue, while dressed head to toe in white, should put that to rest.
Brown also posted a photo from the night out, showcasing her and her cohort for the concert. The 15-year-old actress is currently in the U.K. filming Enola Holmes, an upcoming movie about Sherlock Holmes' mystery-solving younger sister.
See more news on Grande and Styles below.