Looking swell: Helena Bonham Carter displays her bump

The 41-year-old English star and her film director partner Tim Burton are "very happy" about the addition to their family, said a spokesman.

Miss Bonham Carter, who appears in the latest Harry Potter movie, met Burton - her partner of six years - during the filming of Planet of the Apes, which he directed.

The couple's relationship is less then conventional. They live in separate homes in North London - connected by a secret adjoining corridor.

The actress, who is due to give birth at the end of the year, displayed her bump during a holiday in Italy with Burton and their three-year-old son, Billy. She paddled in the Mediterranean and went for gentle swims.

While his family splashed around, 48-year-old Burton - wearing a pair of goggles on his forehead and a pair of skull-embossed Hawaiian shorts - looked on proudly, taking photographs on his digital camera.

"Helena, Tim and Billy were having a whale of a time," said an onlooker.

"They were laughing, joking and generally fooling around for the entire afternoon - they really are a close family unit. They are also incredibly well-matched in their eccentricity.

"While Helena was wandering around with an assortment of hairclips and flowers in her tresses, Tim refused to remove his goggles - even when he was sunbathing.

"Helena made no effort to disguise her bump and was gently stroking it throughout the day.

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A reassuring pat on the stomach as Helena takes a dip with Tim Burton

Spot on: Helena keeps warm after taking a dip

"She looked keen to keep active though and went for frequent dips in the sea, doing gentle breaststroke laps."

Speaking of her desire for another baby earlier this year, the actress joked: "We've got to get on with it. Todo list: Have sex. At right time."

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Expecting: Helena Bonham Carter is pregnant with the couple's second child