LONDON, May 23 (Reuters) - British actor Roger Moore, who won international fame playing secret agent James Bond, died on Tuesday aged 89, his family said on the actor's official Twitter account.

His 12 years as James Bond, the British agent with a voracious appetite for danger and sex, made Moore a millionaire and a heartthrob the world over.

"It is with a heavy heart that we must announce our loving father, Sir Roger Moore, has passed away today in Switzerland after a short but brave battle with cancer," his three children announced in a statement on the Twitter account.

The son of a London policeman, Moore once said the upper-crust image he portrayed both on and off the screen was a carefully nurtured cover for his shyness and timidity. He also said he was terrified of playing the sex scenes which were a key part of the Bond movies.

Moore's big breakthrough as an actor came in 1962, when he won the part of "?The Saint" in a popular television series of the same name. In this role, he honed his image of the urbane Englishman with a stream of damsels to rescue from distress.

In 1973 came the coveted part of James Bond, writer Ian Fleming's action man spy 007, who held cinemagoers across the world in thrall. The Bond films were said to have earned Moore 14 million pounds ($22 million).

He moved to the United States to become a tax exile.

"I don't see why a chap shouldn't do what he likes and live where he wants on his money, and the British government, which allows talent to go abroad because of taxation, has only itself to blame," he said in an interview in 1989.

After handing over the role of Bond to Timothy Dalton, Moore went into semi-retirement, living a millionaire's life and travelling between his homes in Los Angeles, Switzerland and the south of France.

In 1991, he became an ambassador for the United Nations Children's Fund.

Moore is survived by his fourth wife, Scandinavian socialite Kristina "Kiki" Tholstrup, whom he married in 2002.

(Writing by Gareth Jones; Editing by Louise Ireland and Hugh Lawson) ((gareth.jones@thomsonreuters.com; +49 30 2888 5214; Reuters Messaging: gareth.jones.thomsonreuters.com@reuters.net))