Alexander, Duke of Schleswig-Holstein-Sonderburg, (20 January 1573 –13 May 1627) was a Danish nobleman. Alexander was born in Sønderborg (German: Sonderburg) in Schleswig, the third son of John II, Duke of Schleswig-Holstein-Sonderburg and Elisabeth of Brunswick-Grubenhagen. Because his elder surviving brother chose Ærø as his seat, Alexander received Sønderborg upon their father's death and was in practice its second duke. Alexander died in Sønderborg.

Marriage and issue

Alexander married Dorothea of Schwarzburg-Sondershausen, daughter of John Günther I, Count of Schwarzburg-Sondershausen, on 26 November 1604 in Oldenburg. They had eleven children:

Ancestors