Elon Musk was such good friends with Sergey Brin, the founder of Google, that he used to crash at his Silicon Valley home on the way to becoming the richest person in the world.
Like any good pal would, Brin even lent Musk $500,000 to pop up Tesla in the early days. In return he received one of Tesla's first all-electric sport-utility vehicles.
But the bromance has unravelled, according to friends, after Musk, 51, allegedly had a brief affair with Brin's wife in December last year.
Brin, himself the world's eighth richest person, and Nicole Shanahan were separated at the time, but living together still, the Wall Street Journal reported on Sunday. Brin filed for divorce in January, weeks after he learned of the brief affair, friends said.
Shanahan - who met Brin on a yoga retreat seven years ago - is seeking $1 billion from the divorce, friends claimed, a fraction of Brin's $95 billion fortune.
In early July Shanahan told the news website Puck of the divorce filing: "I hope for Sergey and I to move forward with dignity, honesty and harmony for the sake of our child. And we are both working towards that."
Rift manifests in corporate dealings
According to the Wall Street Journal, the rift between the two men has manifested itself in their corporate dealings – with Brin instructing his financial advisers to sell his personal stake in Musk's companies.
Neither Musk, Brin, nor Shanahan has commented on the allegations.
The reports are just the latest chapter in a tumultuous year in the spotlight for the world's richest person, after recent reports he secretly fathered twins and has been engaged in a bitter fight with Twitter over his aborted attempt to buy the social media platform.
Earlier this month it emerged that Musk had become the father of two children with Shivon Zilis, an executive at Musk's neurotechnology firm Neuralink.
The twins were born last November. Then in March this year, Musk welcomed a second child born to his musician girlfriend Grimes.
Called Exa Dark Siderael, of Y for short she was a sister to "X Æ A-12" – or X – who was born two years earlier.
Now a proud father of nine, Musk, hailed his growing brood on Twitter.
"Doing my best to help the underpopulation crisis," he wrote. "A collapsing birth rate is the biggest danger civilization faces by far."
Musk, whose businesses include space exploration company, SpaceX, has undergone a similarly turbulent time in his corporate affairs over the last few months.
Only last week his decision to stall on a deal to buy Twitter for US$44 billion triggered acrimony and aggressive litigation with the social media giant urging a court in Delaware to force Musk to complete the takeover.
He had pulled out of the deal complaining about the number of fake and spam accounts on the service.
Earlier this month it emerged that Tesla had been hit hard by a spectacular fall in the company's bitcoin investments.
Musk had invested $1.5 billion in the cryptocurrency, moving part of Tesla's cash reserves into Bitcoin.
The bet backfired spectacularly, costing the company an estimated $440 million.
Tesla itself has run into trouble as the company faces competition from other car manufacturers moving into the electric vehicle market.
And late last month Tesla was sued by two former employees who accused the company of illegally laying off staff without notice.
Musk, who said he had a "super bad feeling about the economy" said the firm needed to shed 10,000 jobs – about a tenth of the workforce – to cope.
Musk has also recently been accused of exposing himself to a flight attendant at his aerospace company, SpaceX, while on a flight to London, an allegation he has denied.
World's top richest men
• Elon Musk - $242B
• Jeff Bezos - $146B
• Bernard Arnault - $137B
• Gautam Adani - $112B
• Bill Gates - $112B
• Warren Buffett - $99.6B
• Larry Page - $98.7B
• Sergey Brin - $94.6B
• Larry Ellison $92.8B
• Steve Ballmer $92.1B