Veteran broadcaster David Dimbleby has called for the monarchy to be more "in tune" with the country.
The 87-year-old believes that Prince William will need to make "radical alterations" when he succeeds his father as the King.
Mr Dimbleby spoke out this morning ahead of his three-part documentary, airing on the BBC, which will look into the Royal Family's remaining power.
Speaking to BBC Radio 4's Today programme, explaining how the monarchy will have to adapt to survive, but does not believe Britons would vote to remove it altogether.
Mr Dimbleby has called for the royal family to be more 'in tune'.
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He said: "The idea of a republic, I was thinking about it.
"To find a president that would suit England, Scotland, Wales and Northern Ireland, I'm not sure it is easy as the Republican movement think.
"So I suspect our future is a monarchy, but it does need to be a monarchy that fits the 21st century; it can't be one that is just, you know, a flamboyant display of power and wealth.
"It has got to change in some way so that it is more in tune with a country that is, after all, no longer top dog and maybe can no longer quite sustain that level of grandeur."
Mr Dimbleby said he 'is not sure it is easy' to back a Republican movement.
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Mr Dimbleby suspects that King Charles may not have given up pushing his opinions in private, who, as the Prince of Wales, was renowned for expressing forthright views.
He said: "I am interested that he may not quite have abandoned it, and I am curious about the role that he plays.
"But, as I say, William certainly seems to take a different view; we don't yet know what it is."
The broadcaster explained how he was shocked when he studied the workings of the monarchy for his new series.
The broadcaster believes that Prince William will need to make 'radical alterations'.
| GETTYMr Dimbleby said: "Almost everything surprised me, because I had never really looked at it in depth.
"And we had wonderful interviews with the most senior members of the Palace hierarchy, the private secretaries to the Queen, about moments when they thought they had got it a bit wrong, Diana's death, for instance.
"They have a wonderful way of talking about it, 'we were a bit behind the curve'."
Prince William insisted that he will not be afraid to make tricky decisions as king, telling actor Eugene Levy that "change is on my agenda".
William has already said that 'change is on my agenda' when he becomes king.
| PAThe broadcaster said: "What William's on about is, if the monarchy is to remain popular in the future, it has got to make changes, [there have] got to be some radical alterations.
"I don't know what he is thinking of, but we posit one or two in the [programme]"
The broadcaster's new documentary will study royal finances as Mr Dimbleby claimed King Charles is Britain's "first billionaire" monarch.
He added of the Royal Family: "They have a load of concessions about money, the tax that they pay voluntarily, taxes that they don't pay and I look at all that, and the workings of the Duchy [of Cornwall] and the way that money is spent, and how the duchies operate, it is all contentious matters that people have looked into but I think is interesting."
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