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The monarch regards this as an asset, perhaps seeing echoes of Prince Philip's penchant for jokes. His grandmother has no hesitation in asking Harry to undertake engagements on her behalf, often sending him on tour to nations where his informal style will go down well.
On his Diamond Jubilee tour in 2012, the Prince hugged his way round Belize and Jamaica, where even Prime Minister Portia Simpson-Miller couldn't resist looping her arm through his. Then, he sparked Harrymania again when he arrived in Australia a year later.
To celebrate his milestone birthday, HELLO! takes a look at pictures of the royal at his cheekiest.
- Quoting Bob Marley during tour of Jamaica: "The Queen couldn't be here. So you're stuck with me … But don't worry cuz every little thing's gonna be alright."
- His verdict on an official portrait of him and William: "I don't know, I'm a little bit more ginger in there than I am in real life, I think. And [William] got given more hair."
- Another quip about the Duke of Cambridge's hairline: "I think he definitely is brainer than I am, but we established that at school — along with his baldness."
- Volunteering his brother and sister-in-law for the London Marathon: "I've been trying to get a place for years! What do you have to do? What's fantastic is my brother and his wife will be doing it next year, I think. He's going to have to do it now, won't he."
- On William's views about Harry's trip to the South Pole: "My brother, I think he's just quite jealous I managed to get away from a screaming child."
- On looking after Prince George: "I only hope my brother knows how expensive my babysitting charges are!"
- On his nephew's progress: "He's growing up, he is walking and he has big, chubby cheeks. He looks like a young Winston Churchill".
- To the press pack who had gathered to see him do target practice at a shooting range: "You're at the wrong end. Anyone with a camera want to stand at the other end?"