Musk’s denial comes after the Wall Street Journal on Sunday, July 24 reported that his friendship with Brin had ended over the alleged affair with Nicole.
Citing people familiar with the matter, the Wall Street Journal said that Musk was engaged in a brief affair late last year with Ms Shanahan.
This prompted Brin to file for divorce earlier this year, ending the long friendship between the two high-profile technology billionaires, the paper also said.
Replying to a link to the story posted on Twitter on Monday, July 25, Musk referred to the report as “total bullsh*t”.
Musk then added that he is still friends with Brin and that they were “at a party together last night!”
Musk tweeted “I’ve only seen Nicole twice in three years, both times with many other people around. Nothing romantic”.
In another tweet, Musk said “WSJ [Wall Street Journal] has run so many bs hit pieces on me and Tesla I’ve lost count.”
Musk, the owner of SpaceX is also in a legal fight over his abandoned plan to buy Twitter for $44bn (£36.7bn) who is suing him after he announced he was walking away from his proposed takeover of the firm.