Paul McCartney and Nancy Shevell engaged

Paul McCartney is set to marry his girlfriend of four years, Nancy Shevell.

A source close to the New York businesswoman told People magazine: "Nancy and Paul are getting married. Ring and all – very exciting."

The couple started dating in the summer of 2007, and were most recently seen together at the Met Gala on Monday (pictured).

It will be the third time that the Beatles star, 68, has walked down the aisle.

He was married to American photographer Linda McCartney from 1969 until her death in 1998 – the couple had four children together.

Then in 2002 he wed Heather Mills, a marriage that ended acrimoniously in 2008.

But despite that troubled relationship, Paul has remained optimistic when it comes to matters of the heart.

"I just like being in love," he said of his blossoming romance with Nancy, 51, in 2008.

Photo: © Rex