"We have a long way to go," Hearn said.
Parker and Joshua have looked likely to meet in the ring sooner or later over their young careers, with Parker having the mandatory challenging rights to the Britton's IBF title.
A fight looked like it may have come out of that, however Parker's handlers saw the opportunity to claim the WBO title, which he did against Andy Ruiz in December 2016.
"I think that was probably the right decision at the time, certainly a lot easier," Hearn told Stuff.
"It has been a long process but it is the perfect fight for everybody. I feel it's a fight that deep down everybody wants so generally when that happens, as long as everybody is sensible, you'll get there in the end.
"Joseph Parker is going to make a lot of money and so is Anthony Joshua. But more than that, they are going to get a chance to unify the division."