The Duke of Cambridge has confessed to US president Barack Obama that in the "chaos" of the maternity delivery room he forgot to ask if Prince George was a boy or a girl.
William joked about omitting to question medical staff about the one thing the world wanted to know as he chatted with the American leader in the White House's famous Oval Office.
While William was meeting arguably the world's most powerful man Kate, who is five months pregnant, was in New York and in the eyes of a group of young children had been transformed into Princess Elsa from the smash animated movie Frozen.
The youngsters aged three and four, who are receiving help for developmental problems at Harlem's Northside Centre for Child Development, believed Kate was the cartoon character - and shouted "Princess" when asked who had walked into their classroom.
Rose Ann Harris, the institution's director of early childhood services said about the children: "When they heard she was coming they thought it was Elsa - we said a Princess and they got a Princess.The Cambridges are in America on a three-day visit and the Duke flew to meet President Obama ahead of giving a major speech in Washington on combating the illegal trade in wildlife."
William joked with the US leader about George's birth saying: "I didn't work out whether it was a boy or a girl.
"The excitement of the event and everything else was just chaos, so you're suddenly like: 'Actually it's a boy in the end'."
"You forgot to ask?" Mr Obama said through laughter.
With the Duchess expecting their second child in April and the Duke due to visit Japan and China early next year William told the president "it's going to be interesting next year" adding: "It's going to be a busy year next year, but good."
The Prince sat next to Mr Obama in front of the Oval Office fireplace, a seat often used by visiting presidents and prime ministers.
Both men smiled and look relaxed and the US leader showed no signs of the discomfort that led him to be treated for acid reflux over the weekend.
The two men last met at Buckingham Palace in May 2011 during a state visit by the President to Britain.
William is passionate about trying to preserve the planet's most endangered animals and habitats and founded the umbrella organisation United for Wildlife to try and tackle the issue and other problems.
He used his major speech on the illegal wildlife trade in Washington to announce that a taskforce, chaired by former Foreign Secretary William Hague, would be established to examine the transport industry's role in the illegal wildlife trade and identify ways "the sector can break the chain between suppliers and consumers".
The Duke, who addressed delegates at the World Bank Group's International Corruption Hunters Alliance Conference, said it would be set up under United for Wildlife.
He added: "The task force will bring together key partners and representatives of the transport sector, underpinned by expert legal advice.
"It will draw together existing evidence and information about the illegal wildlife trade, identify gaps in knowledge, and commission research to plug those gaps.
"The taskforce will call on companies to implement a 'zero tolerance' policy towards the trade. Criminals are able to exploit weak and corrupt standards, so we must raise those standards, collectively."
William gave the example of Air New Zealand which he said had "set an important precedent on the transport of wildlife parts by banning the carriage of all shark fins on its planes - whether or not it was legally obtained".
Before giving his speech William wrote about the issues behind his passionate interest in helping to end the trade in illegal wildlife.
In an article written for the blogging website the Huffington Post and headlined "Why we need a truly international approach to tackling illegal wildlife trade," the Duke spoke about why he felt moved to act.
He said: "Many people might wonder why conserving wildlife should be considered so important when there are wider issues of global and national interest, such as conflict and poverty to worry about. The answer is because these issues are interlinked.
"Wildlife crime goes well beyond just a threat to endangered species but also has impacts on our society, economy and security. It undermines efforts to uphold the rule of law, acts as an agent for corruption, creates a barrier to development and fuels global instability."