The corporate lawyer quit her role as Lord Alan Sugar's aide in 2009, leaving to concentrate solely on her PhD in papyrology.
Her former colleague Nick Hewer, who was back on-screen in the new series which began last night, tweeted: "I am pleased to announce that Margaret Mountford may henceforth be addressed as Dr Mountford, as she passed her exam with elan. At last."
Sugar responded: "Congratulations to the now Dr Margaret Mountford for passing all of her exams. Well done."
Announcing her exit from the BBC One show, the 60-year-old said that the competition "took up a large chunk of time each year, and that's time [she] could, indeed should, be spending on [her] studies".
Hewer, who is currently hosting Channel 4's Countdown, recently confirmed that Mountford would make an appearance in the show's Dictionary Corner.
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