Nicole Scherzinger and Lewis Hamilton have reportedly called off their relationship once again, after the Formula One racer refused to marry the singer.

The duo has had a roller coaster relationship over the last seven years, and it is Scherzinger who walked away after a series of rows, reports femalefirst.co.uk.

According to a source, Scherzinger is keen to marry Hamilton and has grown tired of waiting for it.

`It really is over this time,` The Sun newspaper quoted the source as saying.

Scherzinger and Hamilton are said to be spending less time together after Hamilton, who bagged his second F1 championship last year, revealed plans to go for a third, and Scherzinger joined the West End production of musical "Cats".

The source added: "They'd been fighting for months but things had got much worse. They spend so much time apart that things just became untenable."