NEW YORK (BLOOMBERG) - Google co-founder Sergey Brin has instructed his advisers to sell his personal investments in Mr Elon Musk's companies in recent months after learning that the Tesla co-founder had a brief affair with his wife, according to the Wall Street Journal (WSJ).

Mr Musk had an alleged liaison in early December in Miami with Ms Nicole Shanahan, WSJ said, citing unidentified people familiar with the matter.

That ended the long friendship between Mr Musk, 51, and Mr Brin, who helped support the electric carmaker during the 2008 financial crisis.

Mr Brin, 48, filed for divorce from Ms Shanahan in January.

The size of Mr Brin's personal investments in Mr Musk's companies is not known, and it is unclear whether there have been any sales, the newspaper said.

Mr Musk is the world's richest person with a US$242 billion (S$336.2 billion) fortune, according to the Bloomberg Billionaires Index.

Mr Brin is the eighth wealthiest, with a net worth of US$94.6 billion. The affair is the latest in a string of revelations about Mr Musk's personal life.

Reports earlier this year said Mr Musk became the father to twins born to a senior executive at his artificial intelligence start-up Neuralink.

Another of his companies, SpaceX, paid an employee US$250,000 to settle a claim she was sexually harassed by Mr Musk in 2016, according to Insider.

Mr Musk said the accusations were "utterly untrue" and designed to interfere with his acquisition of Twitter, an agreement that he is now trying to exit.

Mr Musk's affair with Ms Shanahan took place in December at Art Basel in Miami, and Mr Musk at another event asked Mr Brin for forgiveness, according to WSJ.

Mr Brin and Ms Shanahan are currently negotiating a settlement, with Ms Shanahan seeking more than US$1 billion, WSJ said, even though there is a prenuptial agreement.