PUBG introduced its game previous year and it became a huge hit as players embraced the Hunger Games-style concept in which 100 players race to kill each other until there's a sole survivor.
I don't think anyone really took Bluehole Vice President Chang Han Kim when he threatened that the company would look at pursuing legal action against Epic Games over the similarities between PlayerUnknown's Battlegrounds' take on Battle Royale and Fortnite: Battle Royale's opportunistic jump into the genre. It has a similar concept, but adds a building mechanic to the mix. Both games share bandaging, reviving and a handful of weapons (such as the SCAR), among other examples.
Epic Games has not yet commented on the lawsuit.
"We filed the suit to protect our copyright", the company told the Korea Times.
There's also no arguing that PUBG, which stands for PlayerUnknown's Battlegrounds, came first.
This new suit is unusual because both companies are partly owned by technology giant Tencent.
PUBG's popularity has been declining since the beginning of this year, while Fortnite has continued to pick up steam.
On Tuesday, PUBG had around 27 000 viewers on streaming platform Twitch, about a tenth of Fortnite's 260 000. "Players have rightfully called us out for failing to address complaints about performance, and recently we haven't done the best job of communicating about the changes we're making to the game". PUBG has been purchased by 44m people since its release in March 2017, implying potential revenue of up to $1.3bn, according to data site SteamSpy.
They've already sued copycat mobile games, which is fair enough as they really are pretending to be PUBG, but despite sharing the same basic premise Fortnite is obviously a very different game.