Facebook creator Mark Zukerberg, with his girlfriend Priscilla Chan.

Microsoft founder Bill Gates had a slip of tongue when he said his pal and Facebook founder Mark Zukerberg had gotten engaged with his Chinese-American girlfriend Priscilla Chan.

Gates revealed the secret when he was speaking to London's Daily Mail.

'His fiancee Priscilla thought about education and he gave money to Newark, New Jersey, and we did a co-grant so that some of our people who had some expertise in that field could help him out".

But the news was rebut by Facebook's head of communications Elliot Schrage in a requiry from Henry Blodget at Business Insider.

"If [Mark is engaged, Bill Gates] knows something I don't know. Gates's communications guy just wrote to apologize for the misunderstanding," Schrage said.

Zuckerberg, 26, has been dating Ms Chan, 26, since they were studied at Harvard in 2003.

The couple currently live in a US$7 million house in Palo Alto, California, which the young billionaire purchased last month.

Facebook creator Mark Zukerberg, with his girlfriend Priscilla Chan.