German car makers used monkeys caged in gas chambers to try and prove their diesel engines were clean, according to a new Netflix documentary.
Dirty Money revealed the "repulsive" animal testing was carried out by a research group funded by Volkswagen, BMW and Mercedes (Daimler) in 2014.
But the clean air study was actually a fraud with one of the cars - a VW Beetle - reportedly fitted with the diesel cheating software meaning it was belching out 40 times over legal limits.
Testing of the 2013 Beetle and a 2004 Ford F250 pick-up by the Lovelace Respiratory Research Institute in Albuquerque, New Mexico was originally due to use humans pedalling on exercise bikes.
But the study was changed to feature 10 monkeys watching TV cartoons in airtight gas chambers with diesel fumes directed through a series of tubes.
The findings were never published and all three car makers have now distanced themselves from the testing process.
The £500,000 ($700,000) funding came direct from the three firms via a not-for-profit organisation called the EUGT - disbanded last year.
A Volkswagen Group statement said: "Volkswagen Group explicitly distances itself from all forms of animal cruelty. Animal testing contradicts our own ethical standards. The EUGT has been in liquidation since June 30, 2017.
"We are conscious of our social and corporate responsibilities and are taking the criticism regarding the study very seriously.
"We know that the scientific methods used by EUGT were wrong and apologise sincerely for this."