Paul McCartney's oldest daughter pregnant

Paul McCartney is set to be a granddad again - after his eldest daughter announced she is pregnant with her third child.

38-year-old Mary - who already has two children, Arthur, 8, and Elliot, 5, with ex-husband Alistair Donald - is expecting her first child with her filmmaker partner Simon Aboud.

A source said: "They don't know whether it's a boy or a girl - and they don't want to.

"Everyone is delighted and they are very happy."

Mary - whose mother was Paul's late first wife Linda - started dating advertising creative director Simon last year after bonding over a mutual passion for the arts.

The source added to Britain's Daily Mail newspaper: "Like Mary, Simon loves photography.

"They don't like a lot of fuss and they often go out separately so as not to draw attention to themselves."

The baby will be Sir Paul's sixth grandchild.

Mary's fashion designer sister Stella, 36, has three children, Miller, 3 Bailey, 1, and two-month-old Beckett, with husband Alasdhair Willis.

Mary and her first husband Alistair, who married in 1998, the year Linda died of breast cancer, officially separated in April 2005 and divorced two years later.