Queen Elizabeth II joined the King of Norway to celebrate the centenary of the Anglo-Norse society, a charity which promotes relations between Britain and Norway.
King Harald V praised Her Royal Highness for her good health.
"She is in great shape," he said.
"It is completely incredible to more than 90-years-old. It is always very nice and to meet her. We talked about everything possible. We are a family."
The night before, Royals from across Europe descended on London to attend the glittering party the Queen threw to honour Prince Charles’ landmark birthday.
According to the Daily Mail, King Harald, 81, thanked the Queen for her hospitality.
“Thank you for a nice party yesterday," he said.
The Queen replied: "I'm so glad Charles enjoyed himself."