Jamie Green will switch from Mercedes to Audi in the DTM next year, as predicted by AUTOSPORT in November.
The 30-year-old Briton has spent his entire career in the series with Mercedes so far and finished a career-best third in this year's championship.
But he believes that a switch to Audi will give him his best chances yet of winning the championship.
"I'm convinced that with Audi, I'll be able to achieve what I've been deprived of so far: to win the DTM title," Green said.
"I really owe my previous employer a lot and making the change after so many joint years has certainly not been easy for me.
"But I carefully considered this step and look forward to a new challenge - I can't wait to sit in the Audi A5 for the first time."
Head of Audi Sport Wolfgang Ullrich said that Green's arrival will strengthen an Audi line-up that is certain to include Timo Scheider and Edoardo Mortara next year.
"There's no doubt about Jamie Green being one of the best DTM racers currently in the field," said Ullrich.
"He proved this in 2012 and was more or less able to choose the manufacturer he wanted to compete for in the DTM - we're delighted that he has opted for Audi and convinced that with his experience and speed, he'll truly be strengthening our DTM squad."
Reports editor Jamie O'Leary
Jamie Green's switch to Audi is yet more proof, if any were needed, that the gentlemen's agreement that existed between Mercedes and Audi for much of the last decade is dead and buried.
The deal, by which neither manufacturer would poach a driver from another, and kept a lid on driver salaries, was blown out of the water when BMW arrived and signed Bruno Spengler and Martin Tomczyk from Mercedes and Audi; the latter just a month after winning the title.
Both men are now earning considerably more from their race activities.
Green is the third man to switch camps since BMW's return to the series and is the first big mover of a winter that could feature a few more.
Significantly his move leaves Mercedes with arguably the weakest driver line-up in the DTM, and that's a big problem for Norbert Haug, Gerhard Ungar and co.
OK, so the signs shown by Robert Wickens in particular suggest that the three-pointed star might just have a new Spengler within its ranks, but it would be neither sensible, nor fair, to promote him to HWA and expect an instant delivery.
Gary Paffett, its only frontline driver, needs a top team-mate to bounce ideas off. It will be to the whole HWA team's detriment if he doesn't get one.
It was interesting to see Bruno Senna, Jerome d'Ambrosio, Robin Frijns, Mike Conway and others get a run-out for the manufacturer at Estoril last week, but such are the techniques required to get the best out of a DTM car, it's unlikely any of these could perform to Green's level in year one.
What Mercedes needs is a frontrunning driver with bags of DTM experience off whom Paffett can bounce ideas. Mattias Ekstrom anybody?