McIlroy grew up in Northern Ireland supporting Manchester United - and you would expect legendary Red Devils captain Keane to be one of his heroes.
But that changed forever when a 12-year-old McIlroy met the former Republic of Ireland midfielder in the early noughties.
Speaking in 2017, McIlroy said: "(Keane) should be one of my heroes as a United player, but I've never liked him since."
The four-time major winner joined Keane and fellow Premier League legends Gary Neville, Jamie Carragher and Ian Wright to retell the story.
Neville immediately asked McIlroy who his sporting idol was - and in a deliberate dig at Keane - the 34-year-old said: "David Beckham."
Read more on Rory McIlroy
Rory McIlroy and Tiger Woods' multi-million dollar bonus infuriates fellow PGA Tour pro
Rory McIlroy finds woman's lap with tee shot and delights crowd with priceless reaction
As everyone started laughing, McIlroy explained: "I was down at Portmarnock Links Hotel and the Irish team were staying.
"I saw one of my Man United heroes in the lobby, Roy Keane, and asked him for an autograph. I was 12.
"He was sitting down, he looked up to me and said, 'Not today, kid.' I was like 'Okay...'"
A guilty-looking Keane immediately asked McIlroy if the story is true - and the golfer insisted it is.
Most read in Football
Transfer news LIVE: Sancho to leave Manchester United, Sheffield United eye Brereton-Diaz
Man United transfer news LIVE: Sancho exit latest, Choupo-Moting and Muller new targets
Brereton Diaz set to finally make Premier League move six months after leaving Blackburn
Moyes with thinly-veiled dig as West Ham prevented from playing Kudus in draw to Brighton
Keane explained: "I was probably in the zone. Probably going to training.
"I always remember in that hotel tell there were kids around annoying the players. Here's another one!"
Rory McIlroy and Shane Lowry lead 'USA is terrified' chant on Team Europe coach in wild Ryder Cup celebrations
Keane added: "I feel bad if that is 100 per cent true. I wouldn't just snub a little kid. F***ing hell, give me a break!
"Can we move on now? Or is this going to be the whole hour-long podcast?"
Despite his comments in 2017, McIlroy admitted he has finally forgiven Keane for his actions.
The golfer said: "I've gotten over it. We've made up now and we're best of friends."
Nevertheless, McIlroy was not done getting his revenge on Keane.
Later in the podcast, Neville asked the Northern Irishman about his relationship with golf legend Tiger Woods.
McIlroy said: "I feel very fortunate. Tiger was my hero in golf growing up and we've forged a really good relationship."
Then, turning towards Keane, McIlroy added: "People always say, 'Don't meet your heroes...'"
As the Overlap crew burst into tears, Keane said: "I knew that was coming! How long have we got left? Speed this up!"
Read More on talkSPORT
Teen voted most likely to be famous at school - now loved by Arsenal stars at Ally Pally
Frank Warren offers alternative opponent to Anthony Joshua following Deontay Wilder loss
McIlroy will have to wait until April to take another shot at golf's elusive Grand Slam by winning the Masters.
But he can now claim to be one of very few people on this earth to make Keane squirm.