Malcolm is said to have a close relationship with the Royal Family and has played alongside Prince Harry at the Sentebale Charity Cup.
From the look of photos of the brother and sister duo, no one had a better time.
Prince George was seen playing with a policeman's kit, as his obsession with officers shows no sign of abating.
Prince George will be king someday, but that doesn't make him immune to a little teasing from his older cousin, Savannah Phillips.
Twitter account Elegantroyals added: 'This was the only disappointing thing about today's polo match.
While Charlotte left us gushing over how adorable she looked even while crying, after she fell from the bench on the Buckingham Palace's balcony, one can not ignore Prince George's naughty antics.
Princess Charlotte, 3, was spotted tumbling in the grass at the event, which was also attended by Princess Anne's grandchildren, Savannah and Isla Phillips, who - with their animated facial expressions - somewhat stole the show at Saturday's Trooping the Colour.
At a reception in March celebrating the Metropolitan Police, one officer joked William's children could join the police cadets, to which the duke is said to have replied: 'Well he does like the police at the moment'.
The incident brought back memories of the 2016 Trooping the Colour when William, 36, was scolded by Queen Elizabeth to stand up.
Kate, who is on maternity leave until the autumn, was relaxed and happy, wearing a £39.99 Zara summer dress.