Prince William visited the island grave of his mother, Princess Diana, on the day that would have been her 40th birthday, reports PEOPLE. William, 19, and his uncle Earl Spencer, 37, rowed out across the 40–ft. lake to the small island, laying a bouquet of white lilies — Diana’s favorite flowers — among the bushes and small trees at the resting place before they stayed there for some quiet contemplation. Dressed in casual clothes William had arrived at the Spencer family home, Althorp, late last Saturday night. Then, he rose early on Sunday to visit the island in the Round Oval before thousands of people were set to enter the estate to pay their respects to Diana. It is rare for Spencer to head out across the water to visit his sister’s resting place, but the emotional pilgrimage was clearly a special time for him and his nephew. Spencer told PEOPLE, “I don’t go over there often, but I go around the lake. The grave itself is not marked — it is nearer the middle. The white stone shows it is a place of burial rather than the actual grave.” He added that he loves “the lake and (to) go and sit and contemplate Diana’s life and all the other things that go on.” Prince Harry, 16, was not with his brother, having opted to remain at home at Highgrove, their father’s house.