Joe Calzaghe's unification bout with Mikkel Kessler will take place at the Millennium Stadium on 3 November.
Kessler (left) could provide Calzaghe with his toughest test
The 28-year-old Dane holds the WBA and WBC versions of the super middleweight title while Welshman Calzaghe, 35, is the WBO title holder.
Both fighters go into the Cardiff bout with unbeaten records.
"This is the only fight I want because a victory over Mikkel Kessler will mean the most to my career at this point," said Calzaghe.
"It will mean more than the beating I gave Jeff Lacy and even more than my win over Chris Eubank, which began my world title reign 10 years ago.
"I'm number one in the division today and I'll be number one in the division after we fight, 3 November can't come quick enough."
Calzaghe-Kessler is probably the biggest and most important fight involving a British boxer since I began promoting
Calzaghe attracted a European indoor record crowd of 35,000 for his 20th defence against Peter Manfredo Jr at the Millennium Stadium in April.
And promoter Frank Warren says he is relishing the prospect of seeing Calzaghe taking on Kessler at the same venue.
"I can't think of two guys who are undefeated and both at the top of the game who are scheduled to meet each other," said Warren.
"The fight is very evenly balanced. I'm excited about it and think it's the best fight I've put together in the last 20 years - there's no doubt about it.
"We're setting the Millennium Stadium out for 60,000 people. We got 35,000 people there last time.
"Outside of the heavyweight fights I've been involved in, this will be the most expensive bout I've put on in terms of purses. This is probably the biggest fight in the world at the moment."
The venue had earlier been in doubt with Warren accusing the Millennium Stadium of greed in negotiations to stage the fight there.
But Welsh Rugby Union group chief executive Roger Lewis had denied this, saying any deal should at least match the deal for the previous fight against Manfredo.
However, a new deal has now been struck and Lewis said: "We are delighted to have brought this great fight to the Millennium Stadium for all the Joe Calzaghe fans in Wales.
"Joe loves fighting in Wales and he loves fighting here at the Millennium Stadium, so we know he will step into that ring with an extra spring in his step."
Calzaghe's fights over the past two years have been shown on terrestrial broadcaster ITV, but Warren's Sports Network has signed a new deal with pay satellite station Setanta.
"I'm delighted to be teaming up with Setanta, who are now major players on the sports broadcasting scene," said Warren.
"I was impressed with their coverage of Ricky Hatton's recent fight against Jose Luis Castillo and know they have a knowledgeable and highly skilled boxing team working for them.
"Calzaghe-Kessler is probably the biggest and most important fight involving a British boxer since I began promoting and having Setanta on board will help make it a show to surpass all others held in the UK."