Tutankhamun's tomb was the most intact ever discovered in Egypt. Close to 2,000 objects were found inside.
But its layout has been a puzzle for some time - in particular, why it was smaller than those of other kings' tombs.
Dr Reeves believes there are clues in the design of the tomb that indicate it was designed to store the remains of a queen, not a king.
His theory has yet to be peer-reviewed and leading Egyptologists have urged caution over the conclusion.