Accompanied by his wife Melinda and three children Jennifer, Rory and Phoebe, the media mogul was spotted arriving by boat to Kjevik, closely followed by the Prince and Princess of Norway and their children.
Mette-Marit's eldest son Marius, 16, along with the couple's children Ingrid Alexandra, 9, and Sverre Magnus, 7, were seen saying goodbye to the Gates children with affectionate hugs while their parents exchanged warm handshakes.
The Norwegian royals are friends with the American millionaire thanks to their work together on global immunisation for the Global Alliance for Vaccination and Immunisation.
Bill and his wife Melinda had landed the day before in Kjevik, and according to the Norwegian press, the family had brunch with the royals in a restaurant in Ny-Hellesund before taking a boat ride.
The couple have paid various visits to Norway and in 2009 were received by King Harald and Queen Sonja in the Royal Palace of Oslo.
This time around the entrepreneur and his family reportedly stayed at the beautiful scenic Storfjord Hotel, owned by British cinematographer Barry Brown. The recently refurbished hotel comes complete with breathtaking views of a fjord and mountains, and has become one Norway's most sought-after retreats.
The visit from the Gates' brood is sure to have made Prince Haakon and Mette-Marit's summer holiday even more special. The couple are already celebrating both turning 40 in the space of a few weeks.
The Prince celebrated his 40th in style, arriving at Skaugum Palace by parachute before enjoying a two-day festival themed party with his family and friends in July. More celebrations are on the way, as his wife Mette-Marit turns 40 on 19 August.