The Kansas City Chiefs fan who partied with three friends later found frozen dead in his backyard was so known for making drug cocktails that he was dubbed “the chemist,” according to a cousin of one of the dead men — who believes the scientist may have “f—ed up.”

“Jordan’s ‘the chemist,’ bro. Jordan’s ‘the chemist,'” Clayton McGeeney’s cousin Caleb told NewsNation’sAlex Caprariello of party host Jordan Willis, who has reportedly since checked into rehab.

“They all knew him as that. It was easy for them to go have fun, but he f—ed up, he made a mistake,” McGeeney alleged of the ongoing mystery, which police have yet to confirm was drug-related.

McGeeney’s cousin was last seen at Willis’ Kansas City home on Jan. 7 to watch the Kansas City Chiefs.

Willis — an HIV scientist — has said he slept for two days without any idea that Clayton McGeeney was frozen dead in his backyard along with Ricky Johnson Jr., 38, and David Harrington, 37.

Asked about who may have brought drugs to the fatal party, McGeeney alleged: “Jordan had ’em. Jordan was the one.”

He alleged Willis was known for years for doling out drugs even before becoming a professional scientist, which he maintained firmly.

“Jordan is somebody that is known from high school as, like, creating drugs for people to make them feel better in certain situations. ‘Okay, well, you wanna do this? I’m gonna make this for you, I’m gonna make this for you’ and handing them out,” he alleged.

“Jordan was the chemist — he’s a scientist, right? He does what he needs to do. And now to use my cousin, my best friend, as a guinea pig? No,” he told Caprariello, shaking his head.

Willis’ lawyer has repeatedly maintained that his client knew nothing of the plight of his friends, whom he had no reason to harm.

His lawyer, John Picerno, did not respond to The Post’s request for a comment on Caleb McGeeney’s allegations.

Willis has entered rehab to address unspecified addiction issues, according to reports.

Police quickly ruled out anything suspicious, stressing that it was not a homicide investigation, much to the anger of some of the dead men’s relatives.

Caleb, however, still has hope for answers.

Everything to know about the 3 Kansas City Chiefs fans who froze to death outside their friend's home

Three Kansas City Chiefs fans were found frozen to death in the backyard of their friend’s home on Jan. 9, where they had gathered to watch a football game.

The bodies of David Harrington, 37, Ricky Johnson, 38, and Clayton McGeeney, 36, had possibly been there for two days.

Jordan Willis, the man renting the home, insisted he had “no knowledge” of the fate of his friends.

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Willis’ lawyer said the man was “asleep on the couch” for two days while his friends’ loved ones frantically tried to contact him.

“This case is 100% NOT being investigated as a homicide,” Kansas City police Capt. Jake Becchina told Fox News Digital.

Here’s more of The Post’s coverage of the tragedy in Kansas City:

• Kansas City Chiefs fan found dead did not use drugs, was ‘murdered,’ longtime girlfriend says
• House where Kansas City Chiefs fans partied has large windows facing yard where 3 froze to death
• 5th Kansas City Chiefs fan at party where 3 friends were later found frozen to death ID’d: report
• Parents of Chiefs fan found frozen to death alongside 2 friends in yard think trio was drugged, ‘dragged’ outside by scientist pal: ‘He concocted something’
• Drugs a possibility in grisly Kansas City Chiefs fans’ freezing deaths outside home, doctor says

“The police are doing their job. If it takes time, it takes time. I will never tell them they are not doing what they should be doing,” he told Caprariello.

“Because you want it to be correct at the end of the day. And that’s what I hope — that when everything comes out, it’s correct,” he insisted.