(CNN) Britain's Prince Charles has spoken for the first time about what sort of king he will be, promising not to meddle in controversial affairs once he takes on the role of the monarch.

In a BBC documentary celebrating his 70th birthday, the heir to the British throne says he will swerve the kind of issues that have brought him criticism in the past.

"You know I've tried to make sure whatever I've done has been nonparty political, but I think it's vital to remember there's only room for one sovereign at a time, not two. So, you can't be the same as the sovereign if you're the Prince of Wales or the heir," said Charles, who turns 70 on November 14.

"But the idea somehow that I'm going to go on exactly the same way if I have to succeed is complete nonsense because the two ... the two situations are completely different. You only have to look at Shakespeare plays, 'Henry V' or 'Henry IV, Part 1 and 2,' to see the change that can take place -- because if you become the sovereign, then you play the role in the way that it is expected," he said.

"So, clearly ... I won't be able to do the same things I've done you know as heir, so of course you operate within the ... the constitutional parameters. But it's a different function."

Charles inspects insects with students as he launches a new charity last year in London's Hyde Park.

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