Sophie, Countess of Wessex, 56, received a royal title upon her marriage to Prince Edward, 56, in 1999. The couple have been working members of the Firm since 2002 and are thought to be the Royal Family's rising stars for the way they have taken on an increasing number of duties following Prince Harry, 36, and Meghan Markle's departure from royal duties.

       Among his many philanthropic projects, Edward is in charge of continuing his late father, Prince Philip's, Duke of Edinburgh Award Scheme legacy and it's long been understood that he would inherit the title upon Prince Charles's accession to the throne.

       If Edward becomes Duke of Edinburgh then his wife Sophie will be Duchess of Edinburgh - a title she may have looked forward to for decades.

       At the time of Sophie and Edward's wedding, the Palace released a statement that seemed to confirm Edward would be the next Duke of Edinburgh.

       The statement read: "The Queen, the Duke of Edinburgh and the Prince of Wales have also agreed that the Prince Edward should be given the Dukedom of Edinburgh in due course when the present title held now by Prince Philip eventually reverts to the Crown.”

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       During a recent interview with the Telegraph, the Countess described the moment Philip asked Edward to take on the peerage in person.

       Sophie said: "We sat there slightly stunned.

       "He literally came straight in and said: 'Right. I’d like it very much if you would consider that.'"

       Explaining the process by which he would inherit the title, Edward added: "It’s a very bittersweet role to take on because the only way the title can come to me is after both my parents have actually passed away."

       He added: "It has to go back to the Crown first.

       "My father was very keen that the title should continue, but he didn’t quite move quickly enough with Andrew, so it was us who he eventually had the conversation with. It was a lovely idea; a lovely thought."

       But doubt has been cast on whether Sophie and Edward will ever become the Duke and Duchess of Edinburgh after insiders claimed it is not in Prince Charles's plans to give out the title once he is king.

       One source told the Sunday Times: "The prince is the Duke of Edinburgh as it stands, and it is up to him what happens to the title. It will not go to Edward.”

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       Another insider said: "Edinburgh won’t go to them [the Wessexes] as far as the prince is concerned."

       Following Philip's death, a constitutional expert explained the process by which the Duke of Edinburgh might pass to Edward.

       Iain MacMarthanne told Express.co.uk: "In 1999, on the occasion of HRH The Prince Edward’s marriage, he was created Earl of Wessex and Viscount Severn, and subsequently Earl of Forfar.

       "It was also announced at this time that in due course Prince Edward would become Duke of Edinburgh."

       He added: "No specific details as to when this would happen, after the death of the Duke of Edinburgh, were given.

       "It remains within the pleasure of the Queen to make a fourth creation of the title duke of Edinburgh, however, it has long been mooted that it will not be until the death of the Queen, and the accession of Prince Charles, that Prince Edward will finally be made Duke of Edinburgh.

       "Royal titles and peerages are not one and the same thing.

       "By George VI’s Letters Patent creating Philip Mountbatten a duke, earl and baron, so the normal rules of primogeniture apply."

       The expert added: "Technically, it will only be when these titles are again assumed into the Crown, on the accession of Prince Charles, that they will again become free to be recreated."

       Sophie and Edward live at Bagshot Park in Surrey with their two children Lady Louise Windsor, 17, and James, Viscount Severn, 13.

       Neither of their children are likely to become working royals and both have been raised as private citizens.