Fashion designer Stella McCartney (search), daughter of former Beatle Sir Paul McCartney, has announced that she is expecting her first child.

McCartney made the announcement Thursday at the launch of her new spring/summer collection during Paris Fashion Week (search). A spokesman for the designer confirmed she was 3 1/2 months pregnant.

The designer told The Daily Telegraph newspaper she did not know whether the baby would be a boy or a girl.

"I want it to be a natural thing," she was quoted as saying. "I want it to be a surprise."

McCartney, 33, married former publisher Alasdhair Willis in August 2003.

The baby will be the third grandchild for the former Beatle — his eldest daughter, Mary, has two boys. Sir Paul's wife, Heather Mills McCartney, gave birth to a daughter, Beatrice, last year.