The couple have called time on their 20-month romance to concentrate on their careers.
In a statement, the pair said: "We can confirm that we have decided to go our separate ways.
"We will focus on our careers at the present time and will remain close friends."
The couple started dating in May 2008 after meeting at the MTV Awards the year before. They were often snapped at red carpet events, and Nicole was a regular fixture trackside at Lewis' Grand Prix races.
But the distance between them – the Stevange-born driving ace is based in Switzerland while Nicole lives in LA – plus their increasingly busy schedules proved too much.
With 31-year-old Nicole away on the Pussycat Dolls world tour for much of last year, it was difficult for her to spend time with Lewis.
And when Lewis celebrated his 25th birthday last month in Switzerland, his girlfriend was in Los Angeles working on her long-delayed solo album.