Thousands of rugby fans are celebrating Wales' Grand Slam 29-12 victory against France in Cardiff.
It is the second time in four seasons the team has clinched the accolade and around 75,000 people were in the Millennium Stadium to witness it.
Many more watched the game on a free big screen in the city's civic centre.
First Minister Rhodri Morgan led tributes to the team saying the Grand Slam would "do so much for Wales as a small country".
Team captain Ryan Jones was presented with the RBS 6 Nations championship trophy by Prince William, who was on his fourth visit to the Millennium Stadium since becoming Vice Royal Patron of the Welsh Rugby Union in February 2007.
The Welsh team were led out by Manon and Gwenan Gravell, the young daughters of late rugby legend and broadcaster Ray.
Describing the performance as "unbelieveable", Welsh rugby legend Jonathan Davies paid tribute to Shane Williams who claimed the Welsh try-scoring record with his sixth of the tournament during the game.
The win also capped a perfect day for a couple who met while watching Wales' Grand Slam win in 2005 and were married in the afternoon before the match.
Michelle Lewis and Matthew Edwards, from Merthyr Tydfil, tied the knot at the town's registry office before heading off to their reception at the Castle Hotel which included a big screen to watch the game.
Mr Morgan congratulated "ruthless" Wales and said the Grand Slam was "even better than 2005!".
"This team is playing with a ruthless defensive efficiency, combined with traditional Welsh attacking flair," he said.
"What Warren Gatland and Shaun Edwards have done is to turn the men in red into men of steel, just like the Welsh teams of the golden years thirty years ago."
"We can now all say proudly that we are the champions of Europe and champions of the Northern Hemisphere. Bring on the Southern Hemisphere."
The Minister for Sport Rhodri Glyn Thomas described the triumph as a "tremendous result for Wales" and said it would be a "real boost to our national self-confidence".
"I warmly congratulate everyone involved with the Welsh team on a marvellous victory to cap a wonderful Grand Slam," said Mr Thomas.
"Warren Gatland and his coaching team must take special credit, but without the efforts of Ryan Jones and the players, such as Ian Gough on winning his 50th cap, that would have counted for little.
"Each one of them can be immensely proud of what they have achieved during this championship campaign and they very much deserve this success."
The stadium roof was closed for the game and Cardiff was lashed by rain throughout the day.
The weather kept down audience numbers at the big screen outside the city's civic centre.
Thousands turned out for a similar event when Wales beat Ireland in the Grand Slam decider of 2005.
St John Wales volunteers, including 140 first-aiders, eight nurses and six doctors, carried out one of their biggest deployments outside Christmas and New Year.