The Stranger Things star and Sia's music video collaborator have been best pals for months, but their first proper get-together was a disaster.

Appearing on Monday's (09Jan17) The Ellen DeGeneres Show, Brown explains, "She (Ziegler) private messaged me on Twitter. I'd never been on a sleepover before and she was like, 'Do you want to come over?' So I'm like, 'Sure, OK'. So I go over and at, like, three o'clock in the morning the fire alarm comes on. We all had to get rushed out of her apartment building.

"I'm crying because I'm like, 'My first sleepover's ruined!'"