When Prince Harry was the cheekiest member of the Royal Family: As he prepares to celebrate milestone birthday... 40 times the Duke of Sussex made us all laugh

Since he married Meghan Markle, he's been striving to be known as a 'humanitarian', mental health campaigner and environmental activist. He studied at the school from 1998, following William who started three years before Harry, wearing a blue school jumper and shorts, peeks through homemade binoculars at photographers after finishing his first day at Mrs Mynor's nursery in Notting Hill, London on September 16, 1987 Prince Harry smiles as a dinner lady kisses his hand during a visit to the Osmani School in London, September 2002 Just six years old, Harry wears a white t-shirt and shorts as he sprints to the finishing line with a big smile during his school sports day on June 11, 1991 Say cheese! Harry cheekily squints during a family photo with his parents and brother Prince William at Kensington Palace, December 1986 The young prince grins as he attempts to balance a bucket of water on his head during a visit to the Osmani School in September 2002 Marking the end of his studies at Eton in 2003, Harry, 18 at the time, smiles next to a bronze statue of Perseus holding the gorgon's head in a garden at the school Princess Diana closes her eyes and Harry grins as water splashes against the pair while they slide down the Depth Charge ride at Thorpe Park, April 1992 With 'Wales' written across his head, Harry stands grinning in a diving suit during a visit to the Royal Navy's fleet diving squadron at Horsea Island, October 2007 Prince Charles picks Harry up to place him on the back of a family dog as King Juan Carlos, his wife Sofia, Princess Diana and William look on during a holiday in Palma, Majorca in 1986 Harry plays with children in South Africa during a visit in 2006 to launch his charity Sentebale. He opens his mouth at a laughing child while another places her hand on his jaw Harry wraps his arm around his cousin Zara Tindall's shoulder, giving her an affectionate hug on the wedding day of Peter Phillips and Autumn Kelly at St. George's Chapel on May 17, 2008 Prince Harry can't help but smile as his aunt Princess Anne presents him with an Afghanistan war campaign, May 2008 Anne playfully picks up a young Harry so he can see over the balcony at Buckingham Palace after Trooping the Colour in 1986 Covered in mud and standing in the pouring ran, Harry grins to his fellow Young England polo players as he waits to receive his trophy after winning a match in 2003 A barefoot Harry, wearing an adorable corduroy dungaree set, takes his first steps at home in the playroom of Kensington Palace in October 1985 Harry, wearing a laidback cap, jeans and unbuttoned shirt, seems to find something amusing at the Guards Polo Club in Windsor, 2004 Harry, with a mischievous grin, holds a child wearing sunglasses and carrying a lollipop during his visit to Lesotho in 2004 Prince Harry makes his grandfather Prince Philip laugh as they watch the Rugby World Cup Final, 2015 Harry, aged eight, smiles while wearing a helmet during a visit with Diana to Germany in 1993 Prince Harry smiles eagerly alongside his brother Prince William on his first day of prep school, September 1989 The young price looks comfortable holding a baby as he makes members of the public laugh during a visit to the University Hospital of Wales in Cardiff in 2008 With a bewildered expression, Harry poses with a copy of Hello! Magazine featuring his brother Prince William and Kate during a visit to University Hospital of Wales on June 5, 2008 in Cardiff Prince Harry, right, playing on a fire engine in Sandringham during an adorable moment with his brother William, 1988 William, Harry and Philip all laugh while the Queen looks somewhat disgruntled during the wedding of Lady Tamara Grosvenor and Edward Van Cutsem, 2004 In a sweet father and son moment, Charles zooms down a slope with Harry on a sled during a skiing holiday in Klosters, Switzerland, 1997 Harry, wearing a 'Haiti we care' t-shirt, shows off his dance moves at a concert in Barbados in aid of the Haiti earthquake disaster in January 2010 Harry takes a call and seals a £10billion City deal during a charity day for international brokerage firm ICAP, 2008.