Now, Liam Payne has dropped the strongest hint yet that the group will reunite to mark their 10th anniversary.
"I'm not allowed to say too much obviously, because I'd be giving it away," he told James Corden after the TV host reminded him of the milestone.
"But we've been speaking a lot more at the moment."
Payne added: "I think that we're all feeling that that 10 year[s] is a very special moment."
The boy band formed on The X Factor in the UK in July 2010.
Payne confirmed he'd had a "beautiful" FaceTime call with Niall Horan and had also chatted with Louis Tomlinson.
The group went on to sell more than 50 million records around the world, with songs like What Makes You Beautiful, Best Song Ever and Story Of My Life.
Things started to unravel when Zayn Malik quit in the middle of a world tour in 2015, citing stress. He later called One Direction's music "generic" and said it didn't suit his tastes.
"There was just a general conception that the management already had of what they want for the band and I just wasn't convinced with what we were selling," he told Fader.
The rest of the band went on hiatus after promoting their fifth album Made In The AM in February 2016, and the break has now lasted for more than four years.
In the meantime, all five singers have launched solo projects with varying degrees of success.
Styles' mystical take on 1970s soft rock has received the most critical acclaim, while Malik's moody R&B singles have registered the equivalent of more than three million sales in the UK alone.
Tomlinson had been the quietest member, releasing sporadic singles and appearing as a judge on The X Factor in 2018. His debut solo album Walls finally arrived earlier this year and entered the top 10 in both the US and the UK.