In a statement to The Independent, Ms Shanahan’s attorney Bryan Freedman said the claim she had slept with the Tesla CEO was “defamatory”.
“Make no mistake, any suggestion that Nicole had an affair with Elon Musk is not only an outright lie but also defamatory,” Mr Freedman said.
The Wall Street Journal reported on Sunday that Mr Musk had allegedly engaged in a brief affair with Ms Shanahan in December 2021. At the time, Ms Shanahan and Mr Brin were separated but still living together.
Mr Brin and Ms Shanahan divorced in January, citing “irreconcilable differences”.
The next day, Mr Musk refuted the claims in a series of tweets.
“I work crazy hours, so there just isn’t much time for shenanigans,” Mr Musk said.
“None of the key people involved in these alleged wrongdoings were even interviewed!,” he added.
He later shared a photo of himself partying with Mr Brin on Twitter.
“This is total bs. Sergey and I are friends and were at a party together last night!” Mr Musk added in a separate tweet.
“I’ve only seen Nicole twice in three years, both times with many other people around. Nothing romantic.”
In a statement, a spokesperson for The Wall Street Journal said: “We are confident in our sourcing, and we stand by our reporting.”
Mr Musk is the richest person in the world, with an estimated net wealth of $219bn, while Mr Brin is 7th on the Forbes richlist with a net wealth of $107bn.