From Camilla's first marriage to Andrew Parker Bowles, King Charles has five royal grandchildren and five step-grandchildren.
At the Sandringham Flower Show in 2013, he appeared delighted to receive a teddy bear for George.
They spoke following a charity polo match in 2015, during which Charles appeared to praise George's shoes.
In June, Prince Louis sat on his grandfather's lap during The Mall's Platinum Pageant to commemorate Queen Elizabeth's platinum jubilee.
At this year's Trooping the Color, 4-year-old Louis seemed to get scared when military planes flew over Buckingham Palace.