The Duke of Cambridge and Prince Harry cracked jokes with each other as they made a record-breaking multibillion-pound deal for charity on a City trading floor.
As the brothers brokered a huge 25 billion euro (£21bn) trade they bantered back and forth with one another, and Harry ribbed William for being preoccupied with "baby chat".
The Princes were at brokerage firm BGC Partners in London's Docklands to raise money in memory of people who died in the attacks on New York's Twin Towers on September 11 2001.
Harry remarked about his brother: "He's on the phone and it's all baby chat."
He then turned to William and said: "Stop flirting, get on with it!"
BGC lost 658 employees in the attack on the World Trade Centre 12 years ago, and its annual Charity Day, now in its ninth year, has so far raised more than 89 million dollars (£56.5m).
All profits from the trades during the course of the day are donated to good causes, including William's SkillForce and Harry's WellChild organisations.
The Princes each made a handful of high-value deals during their 50-minute visit. At first they appeared a little timid, but they soon got into the swing of things as the raucous trading floor buzzed around them.
At one point William remarked to a broker: "B****y hell, was that a billion?"
After the trader nodded, he turned to Harry to say: "Apparently we should work here."