Paul McCartney and Nancy Shevell Are Engaged (Report)

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"They have the right chemistry," an insider says. "They're both cool, chilled out and optimistic."

Beatle Paul McCartney is set to wed his girlfriend of four years, Nancy Shevell, reports.

"Nancy and Paul are getting married," says a source close to Shevell, 51, who sits on the board of New York City's Metropolitan Transportation Authority. “Ring and all – very exciting."

McCartney, 68, met Shevell in the Hamptons in the summer of 2007.

"They have the right chemistry" despite their 17-year age difference, the source said. "They're both cool, chilled out and optimistic."

They last appeared together Monday at the Metropolitan Museum of Art in New York City.

It's McCartney's third marriage.

His first wife, Linda McCartney, whom he wed in 1969, died of breast cancer in 1998.

He went on to wed Heather Mills in 2002. It ended in a messy divorce six years later.

He has five children: Heather, 48, Mary, 41, Stella, 39, James, 33, with Linda and Beatrice, 7, with Mills.