The Duke of Sussex congratulated the South African team after they beat England in the Rugby World Cup Final.
As Prince Harry shared a beer and posed for photos with them he said to Lood de Jager: 'F***! You're so tall'.
After the match the duke praised the England team for an "outstanding job" and urged them to hold their heads high after their dreams of Rugby World Cup victory ended in disappointment.
Harry, who joined Japan's Crown Prince Akishino in the stands for the final in Yokohama, said the players should be "incredibly proud" of their achievement, despite their 32-12 loss to South Africa.
"Tonight was not England's night," the duke said, in a message posted on the Sussex Royal Instagram account.
"But the whole nation is incredibly proud of what @EnglandRugby have achieved over the past few months," he added.
"Hold your heads high boys, you did an outstanding job and we couldn't have asked more from you."
Harry also congratulated the Springboks on their win, saying he could not think of a nation "that deserves it more".
"To the whole of South Africa – rugby unites all of us in more ways than we can imagine, and tonight I have no doubt that it will unite all of you," he said.
Before the match, the duke said the tournament had been "incredible" and predicted the final would be a "fantastic game".
In a video shared by the official Rugby World Cup Twitter account, Harry said: "May the best team win. I think the competition is going to finish the way it started, which is spectacularly."
He added: "The way they (Japan) have hosted this whole competition has been incredible. I think that the way they respect each other, the way that they've respected the game and the way they've respected the travelling teams has been typically Japanese."
Earlier, Harry warmed up for the final at a training session for would-be Japanese Paralympians – and discovered that one or two of them were rooting for England's opponents.
"Who are you guys supporting tonight?", he asked a group of wheelchair rugby players at Tokyo's new Para Arena for disabled athletes.
Back came a chorus of "England" before Tomoshige Kabetani piped up: "South Africa!"
"I'll have a word later," joked Harry. "You might not get selected for the Paralympics!"