The slimmed-down monarchy looks set to get even thinner - and it's one royal who could really bear the brunt of the dwindling numbers. When Prince William eventually ascends to the throne, the ageing working royals may have well slowed down, with only his three children, it seems, that will one day join the ranks.

Therefore, it has long been said that his relatively young cousins, such as Princess Beatrice, Princess Eugenie and even Zara Tindall, could help plug the gap by helping out on an informal basis. It comes as sources close to William reportedly say he has been thinking about his plans for the future as he assesses what is important to him.

But according to Jennie Bond, one key royal who once would have figured highly in these plans, but has no place at all now is his estranged brother Prince Harry.

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And the former BBC royal correspondent told the Mirror : "I don’t think Harry figures in William’s plans at all. It is a very sad situation because Harry was his wingman and would have been the brother he could rely on when he takes on the very heavy responsibility of being King.

"Harry would have had an extremely senior role and been the sibling, friend, supporter and sounding board that the Princess Royal is now to her brother King Charles. It is a great loss for William, but one which I think he has now accepted."

However, one cousin tipped to get a huge role is Zara Tindall, who could take on all royal horse racing matters, which Jennie said would be a stroke of genius from William.

She explained: "There will be so many demands on his time when he is King that I think it’s a brilliant idea – if the reports are to be believed – that he might hand over racing matters to Zara Tindall. Like her mother, she lives and breathes horses; she’s also extremely glamorous and well-liked and it would be a perfect fit.

"I don’t think William or Catherine are particularly interested in the racing world, so it would work out well, although I’m sure they would still trot along to Ascot from time to time. They’d always be sure of a bit of fun and a giggle with Zara and Mike."

In an interview many years ago, William once memorably said that he doesn't lie awake at night thinking about his destiny. But Jennie added: "William wouldn’t be human if he hadn’t thought long and hard about his future role as King and how he will approach it. That much was apparent when he stated that he wanted to do his job 'with a small r'. A tiny phrase, but full of meaning.

"Although he admired his grandmother hugely, and learned a great deal from her about the destiny which lies ahead of him, I think he will continue to build on his father‘s approach: being more than a figurehead or patron, but grappling instead with the nuts and bolts of social issues that need fixing and trying to help interested parties come up with practical solutions.

"William is taking on even bigger social issues: homelessness, mental health and the environment. But he’s not just talking about them, he’s taking action. And he is full of optimism and positivity; striving always to make some impact, get things rolling - even though a complete solution may not yet be possible, it’s all a move in the right direction. Better to do something than nothing. And I think he will continue in this vein when he is King - as much as the role allows."

But like most things, there is a fine balancing act to be struck, and Jennie believes this will be between him moving forward into the modern era, while at the same time retaining tradition.

She said: "I don’t think he is comfortable with all the pomp and pageantry, although I think he will retain the grandeur of great military occasions like Trooping the Colour. I cannot, though, see his coronation being anything like as grand and - let’s face it, frankly really rather bizarre - as that of his father or grandmother.

"He has to strike a balance, I suppose, between the monarchy being absolutely down with the kids, taking selfies and larking around with the crowds, and the dignity of the institution. But I think we will see a King who is immensely relatable – despite his wealth and elite status.

"He has said in the past if he cannot work to make some sort of difference in the world, then what’s the point of him? And I think he’s right. He has to be more than a figurehead, or a mouthpiece for the country in times of crisis or jubilation. He wants and needs to use his platform to make this country a better place to live."