The special adviser to the Duke and Duchess of Cambridge and the Duke and Duchess of Sussex is stepping down from his post.
Sir David Manning, 69, was received by the Queen at Buckingham Palace on Wednesday afternoon upon relinquishing his appointment, the Court Circular recorded.
The key aide joined William and Harry’s household a decade ago in 2009, when the brothers’ royal profile was growing, and he went on to mentor Kate and, more recently, Meghan.
Kensington Palace said William, Kate, Harry and Meghan were “incredibly grateful” for his guidance and paid tribute to “his wise counsel”.
It is understood that Sir David is stepping back now that the couples are well-established in their international work.
His post was seen as unique and so will not be replaced.
A spokesman for the Cambridges and Sussexes said: “Their Royal Highnesses are incredibly grateful for the guidance and support that Sir David has provided over the last 10 years.
“His wise counsel has been central to the success of their international tours and the early stages of their official work as members of the royal family.”
While Sir David is ending his formal role, he will continue to act as a trusted informal adviser, and is said to be close to both couples, and particularly to William and Harry.
A former British ambassador to the US, Sir David was Tony Blair’s foreign policy adviser.
He has mentored William and Harry on a range of issues over the years, including foreign affairs and government matters.
Ahead of William’s marriage, seasoned diplomat Sir David was instrumental in prepping Kate Middleton, now the Duchess of Cambridge, for royal life.
He was seen as a safe pair of hands who could work behind the scenes to guide the future queen, and ensure she was better supported than the late Diana, Princess of Wales had been.
He has joined the Cambridges on many overseas tours, including William and Kate’s first joint trip to Canada and the US, and again on their visit to Australia and New Zealand with baby Prince George.
He planned, and prepared William for, the duke’s sensitive visit to Israel and Palestine in June last year.
Sir David also acted as senior adviser to Harry, and former Suits star Meghan, when she married into the royals in May last year.
The American former actress is likely to have been offered briefings by Sir David on the British constitution.
He was part of Harry and Meghan’s entourage during their tour to Dublin two months after their wedding, and was with them for the Fiji and Tonga leg on their first official long-haul overseas expedition.
The Cambridges and Sussexes have been reported as being set to split their royal household and formally separate their staff within weeks.
Harry and Meghan, who are expecting their first child in late April or early May, are due to move to Frogmore Cottage on the Windsor Estate.
The couple have been living at Kensington Palace in London, near William and Kate and their three children.
The division of the household is reported to be a natural move with the royal brothers’ former double act having developed into two couples and their families.
Sir David was Britain’s ambassador to the US for four years until 2007.
He was Mr Blair’s key aide on foreign policy in the run-up to the 2003 Iraq war and gave evidence to the Chilcot inquiry.
He joined the Foreign Office in 1972 and served in Warsaw, New Delhi, Paris and Moscow, and went on to become ambassador to Israel and the UK permanent representative at Nato.
The court circular, the daily record of royal engagements, for Wednesday read: “Sir David Manning was received by The Queen this afternoon upon relinquishing his appointment as Special Adviser to The Duke and Duchess of Cambridge and The Duke and Duchess of Sussex.”