Background
Cecilia was the daughter of Elector Frederick I of Brandenburg (1371–1440) from his marriage to Elizabeth (1383–1442), daughter of Duke Frederick of Bavaria-Landshut.
Cecilia was the daughter of Elector Frederick I of Brandenburg (1371–1440) from his marriage to Elizabeth (1383–1442), daughter of Duke Frederick of Bavaria-Landshut.
Cecilia"s brothers were the reigning Electors of Brandenburg, first Frederick II and later Albrecht III Achilles. Both couples had been engaged on 3 March 1420. After an exchange of territories, Cecilia received Wolfenbüttel Castle instead.
Bishup Magnus of Saxe-Lauenburg tried to redeem pledges to Duke Henry II, and in particular Wolfenbüttel Castle.
Henry managed to avert the claims of the bishop. A dispute then erupted between Henry and William.
The dispute was settled by dividing the Duchy of Brunswick. Henry received Brunswick-Wolfenbüttel, while William had to make do with the Principality of Calenberg.
Cecilia died on 4 January 1449 and was buried in Brunswick Cathedral
Frederick III "the Restless" (1424–1495), Duke of Brunswick-Calenberg
married firstly in 1463 Princess Anna of Brunswick-Grubenhagen (1415–1474)
married secondly 1483 Margaret Countess of Rietberg (died: 1533 or 1535)
William IV "the Younger" (1425–1503), Duke of Brunswick-Wolfenbüttel
married in 1444 Countess Elisabeth of Stolberg-Wernigerode (died: 1520 or 1521).