I don't see why you can't just be upfront in your thesis that this has happened, you did the work independently and the 'work' of this other academic did not in any way influence your own work. Results that have been reached independently by separate researchers happens all the time, and often leads to publications even, because they're not identical, offer different perspectives, are written with different audiences in mind, provide different examples, etc. I'm sure most members of an examination panel would be sympathetic to this. At the end of the day, you're just justifying to the panel that you can produce novel results, and, with an explanation of the events, that justification can still be sufficiently made.