The All Blacks are scheduled to face Ireland, England and Scotland on successive weekends in November and after months of discussion a November 5 date has been agreed by the New Zealand and Welsh Rugby Unions for the extra Test in Cardiff.
It will be the first time in 17 years that the All Blacks have had the opportunity of facing all four home nations and the match at the Millennium Stadium will also mark 100 years since the first Test between New Zealand and Wales.
Because the match against Wales falls only two weeks after the National Provincial Championship final, All Blacks coach Graham Henry and his management team discussed the issues of player welfare and workload with group of senior squad members.
But they all felt the opportunity of a Grand Slam tour in the same year as the series against the Lions was something not to be passed up.
"This will be enormous and coming at the end of a year in which the All Blacks will take on the British and Irish Lions, means that the All Blacks and our fans face a truly epic challenge," Henry, the former coach of Wales and the Lions, said.
"As for taking on Wales again after their Six Nations win - I can already picture the atmosphere in Cardiff."
Following the Wales match, the All Blacks tackle Ireland on November 12, before taking on England a week later and then Scotland on November 26.