Google pays Apple a whopping 36 percent of revenue it earns from searches made through the Safari browser, a witness accidentally revealed during the company's antitrust trial.
Since 2002, Google has been the default search engine on Apple's Safari browser, an important deal that makes it the de facto search tool on iPhones.
Both companies had sought to keep the financial details of the deal private, but on Monday, Google's economics expert witness Kevin Murphy, a University of Chicago professor, let the figure slip during testimony in Washington DC, according to Bloomberg.
Google's main trial attorney John Schmidtlein 'visibly cringed' when Murphy revealed the confidential number, the outlet reported.
Apple and Google did not immediately respond to requests for comment from DailyMail.com on Tuesday morning.
The revelation came during testimony in the Department of Justice's antitrust lawsuit against Google's parent company, Alphabet.
The US government brought the case over whether Google acted illegally to maintain its dominance of online search and parts of search advertising, including through deals like the one with Apple to be the default search option.
If the government wins, the company may be forced to scrap some business practices that have helped it stay on top.
Last week, Google CEO Sundar Pichai testified at the trial, acknowledging the importance of making its search engine the default in keeping users loyal.
Google, which started paying for default status on devices in 2005, monitored its partners for compliance.