Harry Styles attends One Direction bandmate Niall Horan's concert, sings along to 'Stockholm Syndrome'

The song is from 1D's 2014 album "Four."

Harry Styles has not forgotten One Direction.

The singer swayed back and forth and even mouthed the words to the band's song "Stockholm Syndrome" at former bandmate Niall Horan's concert Tuesday at London venue Co-op Live. The fan video below, posted on social media, shows him enjoying the track, which was on 1D's 2014 album Four.

Both Styles and Horan have had their own successful solo careers, since the group went on a hiatus in 2016. Even before that, the phenomenally successful band, assembled from solo acts on Britain's The X Factor in 2010, had parted ways with one of its members, Zayn Malik. He left the group, which also featured Liam Payne and Louis Tomlinson, in 2015.

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Though they were together for only a short time, One Direction was a phenomenon. They sold an estimated 70 million records worldwide, and their songs have streamed more than 21 billion times, according to the BBC. But Malik left in 2015, and the rest of the members went on hiatus the following year.

Their last album with all five original members was the one with "Stockholm Syndrome."

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They were so successful that Simon Cowell, who was a judge on X Factor, lamented not owning the band's name in June.

"If one of the band members, for whatever reason, say they don't want to tour, it can stop the others [from] touring. So, if it was me who owned the name, it wouldn't be a problem," Cowell said on The Diary of a CEO podcast. "I can be very naive at times, and that was me being very, very naive. So, next time, that will be part of the deal. I have to own the name. They can still make most of the money, but I need to own the name."

The former One Direction members have stayed busy, though, with each putting out solo albums. Styles, for instance, has enjoyed a robust acting career with roles in Dunkirk and Don't Worry Darling, released three solo albums, and had his own tours, on which he's also covered his former band. As he launched a solo string of concerts in 2017, Styles covered "Stockholm Syndrome" himself.

Horan has performed it several times in his The Show: Live on Tour series, named after his 2023 album, The Show. He told Apple Music 1's Zane Lowe in 2023 that he planned to keep One Direction's music in the rotation.

"I've never been one to hide away from it. They're great songs," Horan said. "There’s so many on there that feel like my kind of stuff as well. And it's good to make new versions as well."

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