A spokeperson for the 37-year-old singer, however, has revealed they are not together and that "it was a coincidence" that they attended the same concert.
"It was a coincidence they were both at the same club. Nicole is not back with Lewis," the spokeperson told the Mail Online.
The former Pussycat Doll and the Formula 1 champion where at the club to watch an exclusive performance by John Newman.
The couple's on-off relationship of seven years ended in February
The Sun revealed: "They arrived separately to watch a John Newman performance and sat at different tables. But then they were taken to a private room. John and 5 Seconds Of Summer were in a second one."
Their on-off relationship of seven years came to an end earlier this year, with Nicole insisting it was the right decision during an interview on American talk show The Wendy Williams Show.
The former Pussycat Doll member said, "You know, everything happens for a reason. I'm a girl of faith and a strong believer, and seven years was a long time."
The pair at the Abu Dhabi Formula One Grand Prix in November 2014
Nicole, 37, was spotted in roll-up jeans, a burnt orange coat and a silk blouse from the exclusive Balmain x H&M collection. While Lewis, who recently won his third Formula One championship, opted for black jeans, a red leather jacket, a baseball cap and a gold chain.
Neither of the exes have dated anyone since ending their relationship but Lewis, 30, was linked to Rihanna after the pair were spotted partying in Barbados. However, he denied the rumours, saying, "You know, I've known Ri for a long time."
Lewis told E! "We've been friends for a while. We get to hang out every now and again… otherwise, we're just good friends."