Despite admitting his public campaigning will reach an end at some point, he did defend his activism, insisting: "If it's meddling to worry about the inner cities as I did 40 years ago... if that's meddling, I'm very proud of it".
Charles, who celebrates his 70th birthday on 14 November with a banquet at Buckingham Palace hosted by the Queen and attended by guests including European royalty, maintained he has always strived to "make sure whatever I've done has been non-party political".
The documentary features interviews with his sons Prince William, who said he would like to see his father spend more time with his grandkids, and Prince Harry, who praised his father for walking Meghan down the aisle when her own father couldn't make the wedding.
"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".
"I think that was very touching".
Prince Charles is getting real about his grandchildren... and good for him!
It includes an interview with the prince's wife, the Duchess of Cornwall, who said Charles is driven by a need to help others.
"They were disappointed. Meghan cried, I'm sure, she did cry, and they both said, 'Take care of yourself, we are really anxious about you, '" he said on ITV's "Good Morning Britain" in June.
The Duchess of Cornwall pays tribute to her husband saying that she wishes people got to know him better and his sense of humour.
He said: 'I don't see why the future monarch should be expected to be completely viewless and silent on everything.
"For example, I love Victoria Beckham dresses, but I don't have the long torso to support that silhouette".
Harry, the Duke of Sussex, asked Prince Charles to step in and perform the symbolic role after Meghan's father pulled out for medical reasons.
"He reads Harry Potter and he can do all the different voices and I think children really appreciate that". 'Now he's reached his 70th year it's a flawless time to consolidate a little bit because, as most families would do, you are anxious about having them around and making sure their health's OK - and he's the fittest man I know but equally I want him to be fit until he's 95.
Furthermore, their kids are going to be raised differently, without as much pressure due to the fact that they are not in direct line to the throne of Great Britain as it is the case of Prince William and Kate Middleton's three young ones.