He exclusively told Express.co.uk: “At a time which is undoubtedly a very difficult one for the Royal Family, the Duke and Duchess of Edinburgh, both hard workers who prefer a relatively low profile, are pivotal figures.”
Mr Fitzwilliams described the couple as “indispensable” to the King and the monarchy as their trips abroad, although not as hyped, remain valuable.
He also stressed that they are the only two other senior working royals, after the Prince and Princess of Wales, under the age of 70, who can still carry out engagements and help with the workload as the monarchy’s “slimmed-down” state is suffering, following the latest health woes involving the monarch as well as Princess Kate.
He explained: “With the King receiving treatment for cancer and the Princess of Wales recuperating from major abdominal surgery, much depends not only on the Queen, who is 76 and Prince William, but also on Edward and Sophie who are two of the only four working royals under 70.
“Last year Edward carried out 297 engagements and Sophie 219.”
On Friday, the royal couple melted hearts after Sophie’s emotional tribute to “the most loving of husbands” at an engagement in Leeds.
At the end of the Community Sport and Recreation Awards, the Duchess said he was “the best of fathers, the most loving of husbands and he is still my best friend” and she was “so proud of the man he is”.
Mr Fitzwilliams added: “Sophie and Edward are currently indispensable to the King.
“Their trips abroad are not hyped but they are nonetheless very valuable.
“As Prince Edward turns 60 expect to see a good deal more of them both in the coming months.”
Meanwhile, in newly released images by Buckingham Palace to mark Edward’s 60th birthday, the Duke is pictured wearing a red jumper underneath a dark buttoned waistcoat and smiling with his three dogs, Labrador Teal, cocker spaniel Mole and Labrador puppy Teasel.
The photographs were taken by Chris Jelf on Monday, March 4, at Bagshot Park.
The expert also touched down on whether the Edinburgh children, Lady Louise Windsor, 20, and James, Earl of Wessex would have to take on royal duties in the future.
He said: “Speculation will continue as to whether their children Lady Louise, who is currently at university and James, Earl of Wessex, who is only 16, might take on some royal duties one day.
“It wasn’t anticipated but there is no other obvious way of arranging things unless it was accepted that there would be far fewer patronages and less royal charity work.”
