In an appearance on Jimmy Kimmel Live on Tuesday, the pair discussed how they first hit it off in private Instagram messages before embarking on the journey of owning a National League football team together, before ever meeting in person.
McElhenney, one of the creators and stars of long-running American sitcom It's Always Sunny in Philadelphia, opened Jimmy Kimmel Live by explaining: "A couple of years ago, having never met in person, [Reynolds] and I decided to buy a small town Welsh football team together and now we're business partners, friends and yes, sometimes lovers."
In an appearance to promote the upcoming fly-on-the-wall documentary Welcome to Wrexham, McElhenney joked with Deadpool star Reynolds that he got the latter "addicted" to football before they completed the purchase of the club in late 2020.
McElhenney told his co-chairman: "I am in absolute awe of you. I think over the last year and a half one of the things I've really cherished is becoming one of your closest friends.
"You're the hardest-working person I've ever met in my entire life."
Reynolds told the studio audience that he first messaged McElhenney on Instagram to compliment him on It's Always Sunny in Philadelphia, and that the subsequent friendship "changed my life". He also joked that his wife Blake Lively was not best pleased with the decision to go into business in Welsh football.
He said: "This changed my life because this is what led to us becoming co-owners, co-chairmen of Wrexham Association Football Club. I remember after you'd reached out about this absolutely insane idea and I remember showing up, seeing Blake and saying 'I have bad news and I have really bad news'.
"The bad news is that I've slid into someone's DMs again, the really bad news is that I might have bought half of a fifth tier national football team in Wales.
"We're still working through that one."
He also confessed that he had never been a big fan of watching sports before McElhenney got him into football.
"Now I understand, particularly soccer - or football because it's in Wales - I understand the absolutely gorgeous disaster slow-motion trainwreck that is the sport of football. I'm obsessed."
The pair previewed some clips from the upcoming documentary, which will document the beginnings of the pair's co-ownership of Wrexham.
The clips included their first physical meeting, and their cruel introduction to the offside rule, when Wrexham's 95th-minute equaliser in the FA Trophy earlier this year was ruled out and a stern look from David Beckham curtailed their raucous celebrations in the directors' box.
Welcome to Wrexham will be available to watch in the UK on Disney+ from August 25.