Hull’s lightweight duo have known each other for years but will collide in a fierce battle in their hometown on Saturday night.
Tales of their closeness are wide of the mark, insists Matchroom promoter Hearn, who says their relationship begins and ends with the simple fact that they came up through the same city’s boxing scene.
“There is no friendship to put aside because they???re acquaintances, not friends,” Hearn told Sky Sports.
“They don???t go out together. They don???t go around each other???s houses. They don???t visit each other???s changing rooms before fights. They don???t have a handshake or a cuddle. They???re just from the same town.
“The truth is, they???re not friends. But they don???t hate each other either.
“Everything has always been respectful, but both of them have made comments to me about the other man. I realised they???re not each other???s biggest fans.
“You won???t see hatred and animosity because they do respect each other but they want to bash each other up.”
Olympic gold medal winner Campbell has emerged as a favourite for the Rumble on the Humber and Hearn is intrigued to see whether the 11-0 undefeated pro can impress against his cross-city foe.
While a world championship fight becomes a step closer for the winner, Hearn also believes that bragging rights for the city will also play a major part.
He said: “We don???t yet know how good Campbell is. There???s a chance he is already the best lightweight in the world so, if he is, Coyle has a difficult night ahead of him.
“It???s a fascinating fight because Campbell is the big favourite but Coyle has the bit between his teeth, which makes him difficult to write off.
“It???s a momentous sporting event for the city. You can???t walk down the street without someone asking ???who???s going to win????. If you???re east Hull you???re on Coyle???s side and if you???re west Hull you???re on Campbell???s side.
“The winner of this, I think, will challenge for the WBC title and the loser won???t be competing at world level.??There???s also masses of local pride and neither of them want to walk around town on Sunday having lost.??
“There???s only room for one world-class lightweight in Hull so let???s see who that is…”