The Payday: The Heist - No Mercy level is not a Left 4 Dead prequel, Valve has insisted.
During E3 reports claimed Payday: The Heist's teased Left 4 Dead mash-up was a prequel to the co-op zombie kill 'em up.
But responding to the video, below, that leaked over the weekend, Valve confirmed this is not the case.
"This is a 100 per cent Overkill made mission for Payday: The Heist simply set in No Mercy hospital from the Left 4 Dead series," Valve's Chet Faliszek told Kotaku.
"It is not telling the origins of the Infection and is not canon. There is a little cameo from one of the L4D characters (the comic should give you a hint) and a fun little Easter Egg with a payoff later in Left 4 Dead.
"Just us having some fun with a studio we are friends with and who have also made a great co-op game."
Developer Overkill Software tagged the YouTube video with the following text: "Have you ever wondered how the Left 4 Dead series began? It started with a heist!"
Overkill announced last month that a collaboration with Valve was underway concerning a Left 4 Dead/Payday crossover, though didn't provide details at the time.