Beneath The Planet Of The Apes ends on one of the bleakest notes of any major franchise film, with Charlton Heston being one of the key reasons. The original Planet Of The Apes movie arrived in 1968 and took what could have been a silly premise and made a sci-fi classic from it. The film was also produced during a time when sequels were rarely produced, outside of the James Bond series.

Planet Of The Apes was such a success that Fox wanted a follow-up fast, which would pick up from the original's shocking ending. One early concept was dubbed Planet Of The Men, where Heston's astronaut Taylor would lead an uprising of humans against the apes. This was rejected, and a big issue with the film's development is that Heston had no interest in returning. After being repeatedly asked to reprise his role, Heston agreed to cameo in the opening sequences under the condition Taylor was killed off.

Related: How Planet Of The Apes Succeeded Where Other Modern Reboots Failed

As work continued on Beneath The Planet Of The Apes, Heston's - who had a grudge against Speilberg - role as Taylor was expanded; he disappears when the story begins and reappears in the final act. The plot instead follows a new astronaut named Brent (James Franciscus) landing on the dreaded planet looking for Taylor and forced through the same indignities as Heston in the original. The most significant addition to the sequel are the telekinetic mutants who live in the ruins of New York, who worship the world-ending Alpha-Omega atomic bomb. In what would be an unthinkable move for a modern franchise, Beneath The Planet Of The Apes concludes with the movie's heroes being brutally gunned down, and a dying Taylor intentionally setting destroying, destorying the planet.

Heston Would Only Make Beneath If The Planet Exploded

Taylor detonates the bomb in Beneath the Planet of the Apes

It's almost as shocking as Planet Of The Apes' ending, and as can be summarized from Heston's initial reluctance to return, it was all his idea. The actor agreed to Beneath The Planet Of The Apes on the condition Taylor died and his fee was donated to charity, but while the bomb was always part of the story, it originally wasn't a world killer either. Instead, one version of the script had the bomb wipe out both the mutants and the attacking ape forces in the finale, but that Taylor, Brent and Nova (Linda Harrison) survived and went off to start a new, harmonious society where humans and apes could co-exist.

Heston - already fearing there would be further sequels - instead suggested the Alpha-Omega bomb destroys the whole planet. The studio went along with this concept, and Beneath The Planet Of The Apes closes on the note that violence will eventually wipe out the world. Since the first two Planet Of The Apes - which James Cameron almost remade - movies had already introduced the notion of time travel, producers were able to get around this little problem by sending two surviving apes back in time for 1971's Escape From The Planet Of The Apes, which led to two more sequels, a TV series and more. Heston franchise slaying plan didn't work, though the unexpected darkness of Beneath The Planet Of The Apes still packs a punch.