Injuries and form have conspired against the brothers - who host a podcast together and are naturally great friends - from ever gracing the same field in an AFL game since they were drafted in 2015.
It even led to wild online conspiracy theories and a long-running joke the twins are actually just one person.
But after Ben's off-season move to Essendon from North Melbourne it seems he will finally face off with Harry in Sunday night's blockbuster showdown against Carlton at the MCG.
Star forward Harry described his first meeting with Ben as "surreal".
"If ever there was a week to be a bit cautious (at training), it might be this week," Harry said on Monday when the brothers appeared at a joint press conference.
"I was watching the last couple of minutes of Ben's game (against Gold Coast on Sunday) and had my fingers crossed nothing happened."
Harry (R) says there's be a 'backyard' feel when he faces brother Ben for Carlton against Essendon. (James Ross/AAP PHOTOS)
More than 90,000 people are expected for the match as the two big clubs clash when they are firing at the same time - a rarity through the past two decades.
Essendon sit second, while Carlton surged to fifth after beating Port Adelaide at the Adelaide Oval for the first time.
"It sort of feels right," Ben said.
"It's a pretty big occasion and both teams are going well."
Ben, a key defender, is expecting to mark Harry in Carlton's forward line in what will be an intriguing side-plot to a monster game.
When Ben suggested he would line up on his twin, Harry joked to him that Carlton spearhead Charlie Curnow was "too good for you".
"It's a 50-50 percentage of whether it's Harry or Charlie," Ben said.
"Obviously the modern day you're going to spend time on everyone, so gone are the days where it's purely a one-on-one match-up.
"But we'll definitely be spending some time on each other."
Harry and Ben McKay promoting the Big Freeze with Bec Daniher. (James Ross/AAP PHOTOS)
The twins did play against each other in one game in the VFL, but this encounter will take them back to their childhood.
"There'll definitely be an element of backyard footy when Ben and I line up on each other," Harry said.
"But in saying that, as soon as the ball's bounced, there'll be so much to focus on and so much going on with the game."
The extended McKay family will be in the stadium, likely in a corporate box that Harry was quick to claim he organised.
"There might be a dinner maybe mid-week," Ben said.
"I think they're (family) excited, nervous - a bit of everything.Â
"Mum and Dad will probably enjoy the limelight a little bit."
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