The Duke of Cambridge and Prince Harry cracked jokes with each other as they made a record-breaking multi-billion-euro deal for charity on a London trading floor.
As the brothers brokered a huge €25 billion ($41.2b billion) 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.
"He's on the phone and it's all baby chat," Harry remarked about his brother.
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 US$89 million (NZ$110 million).
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.
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. "200? Done."
The last deal the brothers made was for €25 billion - a world record for a forward foreign exchange.
After the deal was struck, William remarked: "I'm much better at helicopters."
But executive managing director at BGC Xavier Alcan, who listened in on William's phone call, said he did well.
"He was very pleasant and very courteous," he said. "He was making enough effort to concentrate on the decision."
Celebrities including singer Rod Stewart and his wife Penny Lancaster, DJ Sara Cox, actor Idris Elba and singer Cerys Matthews also helped out on the trading floor.