Prince Harry has asked the Duke of Cambridge to be the best man at his upcoming wedding.
Just days after the birth of his third child, the Duke will now be planning a stag party for his younger brother.
Speaking to ITV News Prince William said he was "thrilled and delighted" to be given the position.
Prince Harry is set to wed Meghan Markle at St George's Chapel at Windsor Castle on May 19, and Prince William had been widely expected to fill the role of best man.
On the wedding day, the Duke is likely to be tasked with looking after Ms Markle's wedding ring and is expected to give the traditional best man's speech at the private evening event being staged by Charles at Frogmore House.
Details of Prince Harry's stag-do are likely to be kept tightly under wraps, but the Scottish Highlands is believed to be one of the top choices with bookies as a destination.
The royals know the area well and it will give them the privacy to indulge in outdoor pursuits and keep their antics under wraps.
Announcing the news, Kensington Palace said: "Prince Harry has asked his brother The Duke of Cambridge to be his best man at his wedding to Ms Meghan Markle.
"The Duke of Cambridge is honoured to have been asked, and is very much looking forward to supporting his brother at St George's Chapel, Windsor on May 19.
"Prince Harry served as best man to The Duke of Cambridge at his wedding to Miss Catherine Middleton in 2011."
Despite their public banter, the two brothers are very close, with Prince William revealing that their mother's death "brought them closer" and "uniquely bonded" them together.
The wedding falls on the same day as the FA Cup final, and Prince William has been President of the Football Association for 12 years.
However, the Duke has decided to put his wedding duties ahead of his FA commitments and will not attend the match.
- Watch Harry and Meghan – The Royal Wedding on ITV on Saturday, May 19 - special coverage begins at 9.25am