The youngster took his mother Princess Diana by surprise when he stuck out his tongue at the Queen's official birthday, Trooping The Colour, on the balcony of Buckingham Palace.
"I am who I am. I'm always going to have that little sort of - how do you say? Child streak," Harry, seen here at a charity event with Prince Seeiso of Lesotho, once said.
The royal brothers are incredibly close and William is frequently the butt of his jokes – most of them about his hair loss.
"I think he definitely is brainer than I am, but we established that at school," Harry once said of his older brother. "Along with his baldness."
Prince Harry let his hair down and enthusiastically took part in a Mexican wave, alongside his brother Prince William and Harry's then girlfriend Chelsy Davy at the Concert for Diana, 2007.
The Prince photobombs New Zealand officials at the Commonwealth Games in Glasgow, summer 2014, giving two thumbs up and grinning widely behind the unsuspecting men.
Massey University then shared the snap on their Twitter account. "Royal photobomb alert! Prince Harry with our Prof. Emeritus Gary Hermansson at #Glasgow2014," read the caption.
Princes Harry and William pose for a selfie with Jamal Edwards at Buckingham Palace, in the first ever social hub as part of The Queen's Young Leaders in July 2014.
During a visit to the charity Canine Partners Training Centre, Prince Harry cuddled an eight-week-old puppy called Veyron. The charity teams guide dogs to people with disabilities including injured soldiers - a community that Harry has long supported.
The former soldier, who served in Afghanistan, dared to challenge Olympic sprinter Usain Bolt during a visit to Kingston, Jamaica.
Harry had been asked especially by the Queen to represent her on a Diamond Jubilee Tour of Belize, the Bahamas, Jamaica and Brazil.
The eligible bachelor, who is great with children, embraced his inner kid as he opened a new playground in Newham, London with former mayor Boris Johnson.
The talented polo player regularly takes part in charity matches for his foundation Sentebale, which he set up in memory of his mother Diana. Here he is pictured gently teasing the opposition.