This is one of those stories from British history that has fascinated people down the generations.
In a world ruled by men, two women ascend the thrones of England and Scotland.
Relatives and rivals - Elizabeth I of England and Mary Queen of Scots.
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When Elizabeth succeeded her sister to the English throne, she did so as a Protestant and, seen by many Catholics, as illegitimate.
They believed that she had no right to the throne and looked elsewhere for a champion.
And they didn't have to look far, Mary Queen of Scots was Elizabeth's half-cousin (once removed), the great-granddaughter of Henry VII (Henry Tudor).
Here was their replacement for Elizabeth.
In this episode we explore the undercurrents that drove these two Queens rivalry, which ultimately ended in tragedy.