The Duke of Cambridge and Prince Harry took to the trading floor this morning where they clocked up a world record 25 billion euro deal.
Prince Harry took delight in winding up his brother the Duke of Cambridge over his "baby chat" as they tried their hand at City trading to raise money for charity.
The Princes notched up a record trade for 25 billion euros but still had time to poke fun at each other, and play jokes on professional traders, at the BGC Partners brokerage in London's
They spent around an hour negotiating deals during the firm's annual charity day to raise money in memory of its 658 employees who died in the 9/11 attacks on the World Trade Centre in New York exactly 12 years ago.
During one joint telephone call, Prince Harry complained that the Duke, who became a father in July, was spending too much time talking to traders about Prince George.
He said: "He's on the phone, it's all baby chat."
Asked how baby George is getting on, the Duke told one trader: "He's very well thanks. He's sleeping quite well."
As the Duke chatted to a female trader, Harry told him: "Stop flirting, get on with it."
At one point William remarked to a broker: "Bloody hell, was that a billion?!"
After the trader nodded, he turned to Harry to say: "Apparently we should work here." He added: "I'm much better at helicopters."
During one of his deals, Harry urged the trader on the end of the line to put up more money.
"150? Why don't we make that 200?" he said.
The last deal the brothers made was for 25 billion euros - a world record for a forward foreign exchange.
BGC broker Nick Thompson, 45, from Otley, West Yorkshire, mentored Harry through the deal he made alongside William.
He said: "He was great. He's very laid back about it. He did very well."
During another call, the Duke teased a trader who could not believe he was on the phone to the future king, telling him: "It's all a wind-up, I'm Gary."
Broker Nick Thompson, 45, helped the Princes seal a lucrative deal while colleagues cheered and shouted around them.
He said: "It was interesting listening to them both to see who was more confident. Harry took to it very well."
As the brothers, both dressed smartly in suits and ties, switched from desk to desk negotiating deals with firms including Barclays and Citi, traders gave Harry a baby gro and a teddy bear for his nephew.
Prince Harry spoke to a broker called George and approvingly told him: "A good, strong name."
He egged on brokers to raise the value of deals, calling out figures and lifting his hand to indicate the figure needed to be higher.
"Are you feeling like making some money for charity today?" he asked. "Good. Whatever you're thinking you can double it."
Xavier Alcan, executive managing director at BGC, said: "William was very efficient. He was making enough efforts to concentrate on the transaction with all the noise around him."
The money raised by each charity day is split between several charities in the UK and abroad. The Princes were raising money for SkillForce, of which William is patron, and WellChild, where Harry is patron.
In their biggest deal made together, the pair broke BGC's record for a forward foreign exchange trade, with a 25 billion euro agreement. It is not known how much the deal will have netted for the charities.
Celebrities including the actors Idris Elba, Thandie Newton and David Hasselhoff and the singer Rod Stewart also took part in the event.
The Princes went straight from the BGC offices to Brentwood Cathedral in Essex, to join the Prince of Wales and the Duchess of Cornwall at the funeral of Hugh van Cutsem, one of the Prince of Wales's oldest and closest friends.