Mark Zuckerberg's Girlfriend His Fiancee: Bill Gates

Microsoft founder Bill Gates may have let the cat out of the bag when it comes to Facebook CEO Mark Zuckerberg's marital status. In an interview to an international daily, Gates used the word "fiancee" for Zuckerberg's long-time girlfriend Priscilla Chan.

Gates is close to Zuckerberg, 26, who has pledged to give most of his fortune away and this inadvertent slip may hint that Zuckerberg is already taken.

Discussing their combined philanthropy, Gates 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 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."

The very-possible slip of the tongue, saying fiancee instead of girlfriend, does 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. Zuckerberg and Chan started seeing each other when they were both studying at Harvard University.

Zuckerberg, who is the 52nd richest in the world with his worth at $13.5 billion, is the second-youngest billionaire in the world, according to Forbes magazine. The first spot rests with Facebook co-founder and billionaire Dustin Moskovitz.