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Richard of Bordeaux and Henry Bolingbroke were first cousins, born just three months apart. Their two lives were from the beginning entwined. When they were still children, Richard was crowned King Richard II with Henry at his side, carrying the sword of state: a ten-year-old lord in the service of his ten-year-old king.

Yet, as the animals on their heraldic badges showed, they grew up to be opposites: Richard was the white hart, a thin-skinned narcissist, and Henry the eagle, a chivalric hero, a leader who inspired loyalty where Richard inspired only fear. Henry had all the qualities Richard lacked, all the qualities a sovereign needed, bar one: birth right. Increasingly threatened by his charismatic cousin, Richard became consumed by the need for total power, in a time of constant conspiracies, rebellions and reprisals. When he banished Henry into exile, the stage was set for a final confrontation, as the hart became the tyrant and the eagle his usurper.

Helen Castor tells this story of one of the strangest and most fateful relationships in English history. It is a story about power, and masculinity in crisis, and a nation brought to the brink of catastrophe and disintegration – and then brought back. At its heart, it is the story of two men whose lives were played out in extraordinary parallel, to devastating effect.