Google and Facebook pledged to help one another if they ever faced an investigation into their pact to work together in online advertising, according to a report from The Wall Street Journal on Tuesday.
The story is based on an unredacted version of a lawsuit filed by 10 U.S. states against Google last week that was seen by the Journal.
Google and Facebook reportedly made a deal in September 2018 in which Facebook agreed not to compete with Google's online advertising tools. In return, the social media giant was given "special treatment" when it used them itself, according to the Journal.
The lawsuit reportedly states that Google and Facebook knew their deal could result in antitrust investigations.
A Google spokesperson told CNBC that the claims made in the lawsuit were inaccurate. "The idea that this was a secret deal is just wrong. We've been public about this partnership for years," they said.
Facebook did not immediately respond to CNBC's request for comment.
Read The Journal's full story here.