"Sibylle of Cleves (17 January 1512 – 21 February 1554) was electress consort of Saxony.
Born in Düsseldorf, she was the eldest daughter of John III of the House of La Marck, Duke of Jülich jure uxoris, Cleves, Berg jure uxoris, Count of Mark, also known as de la Marck and Ravensberg jure uxoris (often referred to as Duke of Cleves) who died in 1538, and his wife Maria, Duchess of Julich-Berg (1491–1543). Her younger siblings were two sisters, Anne (later Queen of England) and Amalia, and a brother, William, who became Duke of Jülich-Cleves-Berg." - (en.wikipedia.org 31.01.2020)
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