Audi says its exit from the German DTM series will allow the manufacturer to direct more resources towards Formula E and other "progressive motorsport formats".
Audi's withdrawal from the DTM is another bitter blow for Germany's premiere motorsport series which had to contend with Aston Martin's departure at the end of last season and Mercedes retreat the year before.
ITR chairman Gerhard Berger, who manages the DTM, said he "deeply regrets" Audi's decision which will leave only a single manufacturer - BMW - on the grid for 2021.
"Today is a difficult day for motorsport in Germany and across Europe," said Berger in a statement.
"I deeply regret Audi’s decision to withdraw from the DTM after the 2020 season.
"While we respect the board’s position, the short-term nature of this announcement presents ITR, our partner BMW and our teams with a number of specific challenges.
"This decision worsens the situation, and the future of the DTM now very much depends on how our partners and sponsors react to this decision," added Berger.
"Nevertheless, I fully expect Audi to undertake its planned exit properly, responsibly and in full partnership with ITR."
The DTM's pain will be Formula E's gain as the Ingolstadt firm strengthens its efforts in the all-electric series in the future.
"Audi has shaped the DTM and the DTM has shaped Audi," said Audi chairman Markus Duesmann.
"This demonstrates what power lies in motorsport – technologically and emotionally.
"With this energy, we’re going to drive our transformation into a provider of sporty, sustainable electric mobility forward.
"That’s why we’re also focusing our efforts on the race track and systematically competing for tomorrow’s ‘Vorsprung' (advance).
"Formula E offers a very attractive platform for this. To complement it, we’re investigating other progressive motorsport formats for the future."
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