DIANA KRALL and ELVIS COSTELLO attends the premiere of 'No Direction Home: Bob Dylan'. New York City, USA - 19.09.05

The singers originally thought they were getting one bundle of joy but were shocked to learn that six-month-pregnant Krall is having twins.

Krall, 41, says, "I'm not kidding. I have twins on my mother's side as well.

"We know (the sex) and everyone's been asking me, but we're keeping that private because we just want to have something for ourselves."

The babies will arrive just in time for the couple's third wedding anniversary on 6 December (06).