The 26-year-old has updated his Facebook status to 'in a relationship' to reflect the fact he is taken, reports the Daily Mail. He added that the change had been "long overdue" but did not explain why he had waited so long.
Observers, however, have noted that often when couples become "in a relationship" on the social network and "engaged" status soon follows.
Zuckerberg and Chan, a Chinese-American from the Boston suburbs, started seeing each other when they were both studying at Harvard University.
Following the new update, Chan's Facebook page also revealed that the pair started their relationship on November 7, 2003, just days after Zuckerberg's infamous Facemash stunt at Harvard.
He was nearly expelled from the university after hacking into different colleges' websites and taking pictures of all the female students, placing them next to each other and asking other students to 'rate' their attractiveness.