Bill Gates calls Mark Zuckerberg's girlfriend his fiancee

In an interview to an international daily, Microsoft founder Bill Gates is said to have let it slip that Facebook CEO Mark Zuckerberg is engaged to long-time girlfriend Priscilla Chan.

Reports say Gates used the word 'fiancee' for Chan, hinting that the Zuckerberg is already taken. Gates is friends with Zuckerberg, 26, who has pledged to give most of his fortune away.

When discussing their philanthropic efforts, Gates is believed to have said: "I didn't say to Mark 'Give me all your money!' He was predisposed to do it and he came to me seeking advice. His fiance 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.'

It could have been a slip of the tongue, saying fiancee instead of girlfriend, but the news would certainly add up. Zuckerberg has been dating Chan since 2003. He recently hit the headlines after buying a 5,000 square feet palace in California for $7 million, moving in with Chan soon after.

However, their Facebook profiles reveal a different story. In March, both Zuckerberg and Chan said they were in a relationship with each other. They had already been dating for seven years.

Then, on June 12 - the day the interview was published - Chan's page still showed she was in a relationship with Zuckerberg, while his didn't have any reference to their relationship. It is not clear when the change was made, or why. His page's privacy settings seem to have changed too, since no pictures he's tagged in are displayed on top of his profile.

Zuckerberg and Chan started seeing each other when they were both studying at Harvard University.

Despite his youth Zuckerberg is worth $13.5 billion, making him the 52nd richest person in the world, according to Forbes magazine - the second-youngest billionaire in the world - behind Facebook co-founder and billionaire Dustin Moskovitz.