David Starkey asserts that Elizabeth, in all probability, knew of her sister Mary's death before she was proclaimed Queen in London, and was well prepared for it. And one of the key figures in the smooth takeover of power from Mary to Elizabeth was William Cecil. William Cecil, 1st Baron Burleigh, (13 September 1521-4 August 1598), one-time Protector Somerset's secretary, had known Elizabeth from the reign of Edward VI, if not before. He survived, and managed to prosper, under the Marian regime, becoming Elizabeth's Secretary of State. He remained Elizabeth's chief advisor for most of her reign and became her Lord High Treasurer in 1572.