As heir to the throne, he is forbidden from interfering in the world of party politics.
Yet Prince Charles once campaigned for Scottish nationalism – which is even more remarkable for a man who is set to reign over the United Kingdom.
The Duke of Rothesay’s surprising support for the Nationalists has emerged in a new book, which tells how he campaigned for the SNP in a mock election while a pupil at Gordonstoun School in Moray.
The teenage prince even went round the grounds shouting “freedom for the Scots” and “down with rule from Whitehall”.
Royal author Ingrid Seward was told about the incident by her late husband Ross Benson, who was a classmate of Charles at the school.
She said: “Normally Charles had middle-of-the-road views and was never extreme about anything.
“He prepared his speeches diligently but there was none of the quick flashes of inspired thought or sudden witty comments for which his father is famous.
“But one of the rare occasions when Charles blossomed occurred during the mock elections at the school.
“Charles became a vociferous supporter of the Nationalists.
“Wearing his Stewart kilt, he marched up and down the grounds during the ‘campaign’, shouting ‘Scotland for ever’, ‘freedom for the Scots’ and ‘down with the rule from Whitehall’. Together with his other political supporters, he held aloft a banner saying, ‘Vote for the Scottish Nationalists’.”
Ms Seward added: “Charles went on to have a warm relationship with Alex Salmond and they often shared a dram together.
“Mr Salmond, who also got on well with the Queen because of a shared love of horse racing, took a shine to Charles because he felt that anybody who loved Scotland was OK by him.
“And through what Charles was as doing at Dumfries House, he saw that he really did love Scotland.
“But Charles has never had the he same relationship with Nicola Sturgeon. It is polite and civil but more professional. Maybe if she knew Charles once campaigned for independence the relationship would be warmer – and he’d be more embraced by his ‘fellow Nationalists’.
“Given the current climate for independence, it is very amusing and a little embarrassing.”
Ms Seward added: ”My husband Ross and Charles were members of the same debating society, the ‘Sophists club’, which met at the home of the deputy English master Eric Anderson. They were driven to house by Charles’s detective Michael Varney.
“When Charles spoke in a debate all traces of shyness left him and he was one of the best debaters.
“He loved Scotland, loved wearing his kilt and on last day of school, the Queen came to see him and he wore his Hunting Stewart kilt in her honour.
“He also loved Scottish poetry and Robbie Burns was one of his favourites and had a book of Scottish ballads he would carry around with him and learnt them by heart.”
Charles was a pupil at Gordonstoun from 1962 and it is believed his campaigning for the SNP took place at the school’s mock elections ahead of the real General Election in 1964, won by Labour’s Harold Wilson. The SNP’s leader at the time was journalist Arthur Donaldson.
Charles’s SNP days are detailed in Ms Seward’s new book about his father, Prince Philip Revealed, from Simon and Schuster, price £20.