The Prince of Wales has been appointed as the new Colonel-in-Chief of the Army Air Corps, Prince Harry's old unit.
Prince Harry served with the 662 Squadron, Army Air Corps, in Afghanistan as an Apache pilot.
Prince William was given the role by King Charles in a major reshuffle to the Royals' military appointments.
The Prince of Wales has also been appointed as the new chief of RAF Valley – where he was based during his military service.
The base is where military jet pilots are trained, with Prince William serving there as a search and rescue pilot for three years.
William has also become the Colonel-in-Chief of The Mercian Regiment.
In the reshuffle, the Princess of Wales also became the Commodore-in-Chief of the Fleet Air Arm and Sophie, Duchess of Edinburgh, is now Colonel-in-Chief of The Royal Irish Regiment.
Both of the roles had previously been held by Prince Andrew.
Princess Kate also takes over from her husband William as Royal Honorary Air Commodore of RAF Coningsby, an appointment he held since 2008.
Kate is the new Colonel-in-Chief of the 1st Queen's Dragoon Guards, known as the Welsh Cavalry, a duty which was carried out by her father-in-law Charles when he was the Prince of Wales.
A statement from Buckingham Palace said "the King is pleased to announce further military appointments for working members of the Royal Family" following his accession.
"The new appointments will continue to reflect the close relationship between the armed forces and the Royal Family in His Majesty's reign."