Read about Good Charlotte's visit to a 5 Seconds of Summer afterparty
The band's Joel and Benji Madden have previously written tunes for the Australians.
The pop-punks let Billboard follow them for a day as they promoted their new album 'Youth Authority' on Friday (July 15).
They performed on The Tonight Show, before later checking out the end of 5 Seconds of Summer's gig at Madison Square Garden in New York.
Billboard wrote: "We’re backstage at Madison Square Garden. Young models and their friends make up most of the area. Benji and Joel stop to say hello to every single person there. We talk about religion and children.
"Calum Hood of 5 Seconds of Summer walks up to Joel, and they go back and forth sharing positive remarks. We talk about Twenty One Pilots being the biggest rock band in the world, how it’s weird they can do that without guitars. Calum says 'but they’re different, that’s interesting'. He’s not wrong.
"We head to Dave & Buster's, where 5 Seconds of Summer has a private room reserved. It’s singer Luke Hemmings’ birthday - he’s 20 today.
"He’s not a man of many words; the extent of his interactions include saying thank you and exchanging hugs throughout the back room. Guests of his party are given free gaming vouchers. Drummer Ashton Irwin darts in and out of the space saying things like 'It’s a big night'."
Billboard's Maria Sherman concluded: "I leave. Good Charlotte’s lives are huge and over the top, and the boys of 5 Seconds of Summer are beginning to enjoy the same fame.
"If anything, I’m reminded of what Joel said earlier: that he refers to his past as 5SOS’ future. 'When we were 5 Seconds of Summer', he starts a handful of stories, more than happy to pass on the torch.
"It’s evident that the band wants everyone to do well, to succeed, to be positive forces in an unforgiving music industry. It’s impossible not to believe in them."
Watch Good Charlotte perform live below:
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