Naomi Watts is finding motherhood "hard work".

The "Eastern Promises" star and her fiance Liev Schreiber welcomed their first child together in July, and she admits it is exhausting looking after the baby.

Naomi Watts' trim post-pregnancy figure is all down to "solid underwear." The 39-year-old actress - who gave birth to her first son Alexander Pete with partner Liev Schreiber less than three months ago - admitted appearances can be deceiving and her toned physique was not all down to hard work in the gym.

When asked what her secret was, she joked to People magazine: "I've got a lot of solid undergarments!"