Beneath the Planet of the Apes

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Beneath the Planet of the Apes was the first sequel to the 1968 movie Planet of the Apes. It stars Charlton Heston (although he is in a very small supporting role) and James Fransicus (although Burt Reynolds was originally intended for this role). The military Ape General was originally supposed to be played by Orson Welles.

Warning: Wikipedia contains spoilers

The ending takes place under the planet's surface with a confrontation between an army of apes, Heston and Fransicus, and a mutated white robed people who worship "the bomb". The planet is destroyed by the atomic bomb going off via the hand of Heston.