A man dubbed "the Swiss gigolo" by the German media has been sentenced to six years in prison for defrauding Germany's richest woman of €7 million (SFr10.3 million).

The 44-year-old man, who admitted attempting to blackmail BMW heiress Susanne Klatten for tens of millions more, was also convicted in Munich on Monday of taking €2.4 million from three other women in similar scams.

The man said he met Klatten, 46, at a spa near Innsbruck, Austria, in July 2007 and started an affair.

Using what prosecutors called a well-practised scam, he convinced Klatten to give him €7 million to pay for treatment in the United States of a girl he had seriously injured in a car accident.

He then asked Klatten to invest €290 million in a trust for him, according to the indictment he confessed to on Monday. When she refused, he threatened to release secretly filmed videos of their trysts.

The man demanded €49 million not to tell her family, the heads of her companies and the media. He lowered the demand to €14 million but Klatten went to the police in January 2008. He was arrested shortly afterwards in Austria and has been held in detention since.

Klatten, who is married with three children, is the daughter of BMW magnate Herbert Quandt and holds a 46 per cent stake in the company along with her mother and brother. Forbes magazine listed her as the 68th richest person in the world last year, with a personal fortune of around $9.6 billion (SFr11.2 billion).

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