UFC president Dana White first revealed word of the bout to MMAFighting.com earlier in the day.
Hunt replaces former Strikeforce titleholder Alistair Overeem, dos Santos' initial opponent. Overeem was forced to withdraw because of injury.
Hunt (9-7) put himself in contender status with a third-round technical knockout of Stefan Struve on March 3. The win was Hunt's fourth in a row.
Dos Santos enters the cage for the first time since losing his title by unanimous decision to Cain Velasquez in December. It was the second time the two had squared off; dos Santos (15-2) knocked out Velasquez in the first round on Nov. 12, 2011.
A win over Hunt could land dos Santos another shot at the title, especially if Velasquez retains his belt in the UFC 160 main event against Antonio "Bigfoot" Silva.
Velasquez and Silva meet for the second time inside the Octagon. During their first battle, Velasquez knocked out Silva in the first round.