In this instalment, Tony Robinson goes in search of the truth about one of Britain's most maligned monarchs, Richard III. Robinson investigates whether Richard really did murder his two nephews, the Princes in the Tower, aged nine and 12, before usurping the throne. And if he did, what were his real motives? Robinson finds that much of what has been understood about Richard as historical fact turns out to be at best mistaken, at worst completely fabricated by subsequent generations. But just as his investigation is drawing to a close, an astonishing fact emerges that leads Robinson to question far more than just the received notions about Richard III. It calls into question the whole legitimacy of the last 500 years of British royalty.

• Tony Robinson