Prince William is seen horsing around with his father and brother on the polo field in footage released to coincide with his 21st birthday on Saturday.
William tells his father he needs stabilisers for his horse
Prince Charles becomes the butt of the young princes' jokes in the film.
All three are shown playing polo together, and after the match, William tells Charles: "I'm well surprised you scored a goal, actually."
His father, 54, replies: "I can do it even at my advanced stage of decrepitude."
William asks: "Were you all right keeping up? It was a quick game."
The film then shows him joking about the possibility of putting stabilisers on his father's
Harry winds Prince William up about forgetting his boots
William's brother Harry, 18, joins in the fun, winding up William after he forgot to bring his boots to the match.
"You're an idiot," Harry tells his brother.
William agrees: "That's just about the stupidest thing I could have
Later, when William jokes he should be congratulated for his play, Harry
says: "Shut up, I nearly fell off my horse trying to get you to hit the ball
and you missed it, spoon."
After a long pause, Prince Charles asks: "Spoon, did you say?"
Harry says: "Spoon, it's not a swear word."
"It isn't, I'm sure. I do hope it isn't," his father responds.
Earlier, before the match, in which the Highgrove team beat their opponents
9-4, the boys were seen laughing affectionately at their father.
Harry said to his brother: "Pa's on good form today, isn't he?"
Prince William will be honoured with a gold £1,000 coin
William replied: "When he starts to think he's really funny, you've got to
William's birthday will be commemorated by the release of a solid gold £1,000 coin.
Just 21 Prince William Alderney gold kilo coins will be minted, with the highest value ever seen on a coin.
Their 22-carat gold will give them a price of £14,500 each.
A further 500 silver kilo coins with a face value of £50 are being struck to mark this special occasion, priced at £695.