That came as somewhat of a surprise given it had long been expected that Payne would be with Reynolds and Campbell in the Holdsworth car.
However, when asked why the switch happened, Reynolds refuted that a decision had ever been made on driver pairings.
He said it was always left open until a final decision was made by the team in recent weeks.
Reynolds also said he would have been happy with either of the 'Matts' as his co-driver for the Great Race, although conceded that he is a better physical fit with Campbell rather than Payne.
"At the start of the year everyone assumed things but there was nothing determined in terms of which of the Matts we would be paired with," he said.
"I think they only got together recently to decide what was going to happen.
"I was happy with either one. I really rate Matt Campbell, he's a world-class driver and he's my height and my size. He'll slot straight in and hopefully we won't have to muck around pouring seats, which is one of the worst things to have to do during the year."
Reynolds added that he didn't have a hands-on role in the decision-making process.
"No I wasn't involved in the decision. I'm just another wheel in the cog of motor racing," he said.
Campbell, who was earlier this year announced as part of Porsche's new prototype programme, will be making his fourth Great Race start this year.
He debuted for what became Grove Racing when it was called Nissan Motorsport back in 2016 before joining Triple Eight in 2017.
He then returned to Grove Racing last year alongside Andre Heimgartner.
Payne, meanwhile, will make his main game debut at the Bathurst 1000, ahead of a full-time promotion, likely at the expense of Holdsworth, next year.
