A brief glimpse at a cave painting in Godzilla: King of the Monsters proves that Godzilla and Kong have fought each other before - or, at least, Godzilla fought one of Kong's ancestors - which means that the Godzilla vs. Kong movie is a rematch. Though Godzilla and Kong have fought once before in the 1962 Toho movie King Kong vs. Godzilla, the upcoming film from Legendary is expected to feature their first meeting in the MonsterVerse.
The reveal comes from the credits of Godzilla: King of the Monsters, which offers plenty of interesting details about the aftermath of Godzilla's fight with King Ghidorah, the Titans' impact on the planet, the current whereabouts of Godzilla and his new minions, Monarch's next mission, and of course, Skull Island. Most importantly, the credits directly sets up Godzilla vs. Kong by revealing that new Titans are on their way to Kong's home in the South Pacific.
The final tease of the credits is a cave painting that shows Godzilla fighting King Kong. The painting suggests that, thousands of years ago, Godzilla and Kong came to blows. This would mean that King Ghidorah wasn't Godzilla's only ancient rival. However, there's a problem with what this cave painting seems to reveal. King Kong wasn't even fully grown when he appeared in Kong: Skull Island, which was set in the 1970s. Godzilla: King of the Monsters director and Godzilla vs. Kong writer Mike Dougherty has noted that Kong was just an adolescent at the time.
This means that Godzilla and Kong have never met, and the giant gorilla depicted in the cave painting isn't Kong at all. What would make more sense is that the gorilla Godzilla fought was an ancestor of Kong's. If this were the case, it would indicate that Godzilla and King Kong's species have an ancient - and perhaps even instinctive - rivalry, just as Godzilla had a rivalry with Ghidorah as the planet's alpha predator. It's possible, then, that Godzilla has visited Skull Island in the past and that's why he had been circling around that area according to the Monarch Sciences website; he might have been keeping an eye on the area because of Kong's ancestors.
This sort of history could be the key to the plot of Godzilla vs. Kong. Some have wondered what would motivate Godzilla and Kong, two monsters with heroic tendencies, to start fighting, but the credits of King of the Monsters may have already answered that question. If the two Titans have an inborn hatred of each other, this alone would be reason enough for the two to fight.
