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Princes William and Harry hit the trading floor

U.K. royals Prince William and Prince Harry turned their hands to trading on Wednesday and closed a multibillion-dollar deal … all in the name of charity.

But the brothers took their role seriously, making a number of trades, including a record-beating 25 billion euro ($33.17 billion) foreign-exchange deal.

The royals also found time to joke with each other and fellow traders, while taking part in BCG Partners and Cantor Fitzgerald's annual charity day, which raises money in memory of those who died in the World Trade Center attacks on Sept. 11, 2001.

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Prince Harry teased his brother the Duke of Cambridge—who became a father this summer—for talking too much about his six-week-old son, Prince George.

"He's on the phone, it's all baby chat," Prince Harry said, according to the Telegraph newspaper.

His brother, meanwhile, is reported to have remarked to a broker, "Bloody hell, was that a billion?!"

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Princes Harry & William play stockbroker

A number of celebrities joined the princes at the event, with "The Wire" star Idris Elba causing a stir on the trading floor. And 1980s legend David Hasselhoff also made waves when he turned up accompanied by two "Baywatch babes."

BGC Partners and its affiliate Cantor Fitzgerald, which lost 658 employees in the terrorist attacks 12 years ago, will donate all revenues generated to more than 100 charities worldwide.

"What we do today is: All of our employees, everyone in the world, all these great guys waive their day's pay," Howard Lutnick, Cantor Fitzgerald Chairman and CEO, told CNBC on Wednesday.

Celebrities trading for charity at Cantor Fitzgerald

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"We have great celebrities come in, sports stars, movie stars, musicians, they all come in and make the day," he said. "And all our clients come to our aid—last year we did $12 million of business and gave every penny of that away,"

To date, the event has raised about $89 million for charity.

By CNBC's Katrina Bishop. Follow her on Twitter @KatrinaBishop