Ruiz must have missed the memo.
Before Ruiz and Joshua step into the ring, they will step onto the scale during Friday's weigh-in, along with the full list of fighters on the card. However, it's important to note Valuev was listed as a 7-footer, whereas Ruiz is only 6-2.
Joshua returned to dominance in the ninth round of the fight with a series of heavy jabs landing squarely on Ruiz' head.
The boxing world reacted to Ruiz's dramatic weight increase, including Matchroom Boxing promoter Eddie Hearn, who said Ruiz "probably ate too much on his break". Ruiz has the faster hands and is more fluid than A.J.
Joshua had been widely expected to be lighter than in the first fight but few expected Ruiz to bulk up in such a manner.
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Joshua landed a strong left hook in the sixth but Ruiz Jr would not be dissuaded from plodding forwards and threatening his own punches.
Mexico's first ever heavyweight champion, by the seventh, was getting frustrated and the referee admonished him for more illegal shots.
Joshua was the dominant boxer though, and continued to make good contact with his punches over the next five rounds, seeming to win each of them easily. Joshua then had to absorb even more in the ninth.
Saturday's heavyweight title fight is about as momentous a title bout as the division has seen in several years.
Two scores of 118-110 and another of 119-109 meant the world titles returned to Joshua, who celebrated with his family and embraced Ruiz Jr after the decision.