Fortnite might be the best-known title in the world of Battle Royale-style video games, but it wasn’t the first. PlayerUnknown’s Battlegrounds introduced the concept of a 100-player battle to the death back in March 2017 — a good six months before Epic Games pivoted Fortnite to capitalize on the new trend. Now, the developer behind PUBG is suing Epic Games in South Korean court over claims that they stole intellectual property for Fortnite, according to a report from The Korea Times.

The injunction against Epic Games was first filed in January 2018, but it appears to be gaining momentum. In a statement to The Korea Times, a PUBG official said it “filed the suit to protect our copyright.” Fortnite’s creators haven’t issued an official statement, but Inverse reached out to the company for comment and will update this post if they respond.

Fortnite vs. PUBG: What’s the Difference?

The rivalry between Fortnite and PUBG has been simmering for a while now as the two games compete for attention. PUBG took an early head start and claimed an impressive record of 3.3 million simultaneous players, but Fortnite beat that record in February with 3.4 million concurrents.

Fortnite is also free to play, which gives it a big advantage over its rival, and it’s available on more platforms too. Interestingly, both games also use the same Unreal Engine 4, which Epic Games owns and operates.

From a gameplay perspective, the two titles are also very similar. Both put 100 players together on a map to scavenge for weapons and compete to survive. However, Fortnite features a cartoonish design compared to PUBG’s more realistic graphics. Fortnite also includes a complex fort-building system, which is a major draw despite its sharp learning curve. Meanwhile, PUBG’s big gameplay advantage is the inclusion of vehicles, but that could end soon with the addition for ridable shopping carts in Fortnite.

With Fortnite vehicles seemingly right around the corner, this lawsuit might be PUBG’s last shot at competing, though it’s still too soon to say how this court case will actually play out.