Princess Beatrix (80) has known almost a year old Prince of Wales for a long time. Charles was present at his opening ceremony in 1980, the 50th anniversary celebration in 1998 and his retirement queen 33 years later. He was regular in the Netherlands to commemorate Britain's use of Arnhem in the Second World War, where he also beat Beatrix. Beatrix also met Charles for several visits to the UK.
King Willem-Alexander and Queen Máxima succeeded in congratulating Prince Charles last month when they went to the tea room on their first visit to Queen Elizabeth with her and her wife Camilla in Clarence House.
In addition to Princess Beatrix, Belgian king Philippe and Queen Mathilde, Norwegian King Harald and Queen Sonja are going to the party.