The former Pussycat Doll, 36, and Formula One racer Lewis, 30, have been together for seven years, but have broken up and patched things up at least three times in that space.
Nicole told The Sun the break up had been amicable and the couple had nothing but love, respect and best wishes for each other going forward.
"I'm devastated that it didn't work out," she said. "It was the hardest decision we had to make, but we made it together."
Nicole was pictured looking downcast while arriving at a performance of Cats at the London Palladium yesterday. Lewis, meanwhile, was on the test track in Spain.
They haven't confirmed why they split but sources have suggested it was because Lewis wasn't ready to marry and start a family but Nicole was.
They've both spoken in the past about the difficulties they've faced because of their careers, meaning their relationship has largely been long-distance. Nicole splits her time between LA and the UK, while Lewis travels the world on the F1 circuit.
An interview Nicole gave to The Telegraph before the split was announced has been cited in many reports, as she talks about sacrifices she's made for her career, which included moving to London from the US to star in Cats.
"I look at this as a great blessing for me to be able to take on this role… but I have made sacrifices. This is very time consuming. I've left LA, left all my friends and my family. It's sacrificing your time in relationships, with loved ones, and my work..."
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