Elon Musk had a brief affair with Sergey Brin’s wife last fall, prompting the Google co-founder to file for divorce earlier this year, according to The Wall Street Journal. According to the Journal, the two entrepreneurs were once close friends, but the affair terminated their friendship.

At the time of the affair in December, Brin and his wife, Nicole Shanahan, were separated but still living together, according to a source close to her. Brin, who married Shanahan in 2018, filed for divorce in January, citing “irreconcilable differences,” according to the Journal, some weeks after learning about the affair.

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According to the Journal, Musk apologised to Brin at a party earlier this year, asking for forgiveness for the affair. Brin accepted the apology but isn’t on good terms with Musk, according to sources familiar with the situation, the Journal cited.

Musk and Brin have been pals for a long time, with Musk apparently frequently overnight at Brin’s Silicon Valley house. Brin, worth $95 billion, is also said to have invested $500,000 in Tesla during the 2008 financial crisis when the automaker was battling manufacturing challenges.

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The alleged affair comes at a trying time for the Tesla and SpaceX founder and CEO, who is also the world’s wealthiest person. Twitter sued Musk earlier this month to finish his intended $44 billion takeover of the social media network after Musk informed Twitter that he was terminating the agreement to buy the firm.

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Simultaneously, it was disclosed that Musk and one of his senior colleagues had twins in November. Musk has also been accused of paying a flight attendant $250,000 to settle allegations that he exposed himself to her during a flight.

None of the parties involved reacted to the report immediately.