Background
Philip II was one of the many children of his father Duke Philip I of Brunswick-Grubenhagen and his wife Catherine of Mansfeld (1501–1535).
Duke of Brunswick ruler of the Principality of Grubenhagen
Philip II was one of the many children of his father Duke Philip I of Brunswick-Grubenhagen and his wife Catherine of Mansfeld (1501–1535).
When he died in 1596, the Grubenhagen branch of the Welfs became extinct, whereafter the principality was occupied by Duke Henry Julius of Brunswick-Wolfenbüttel. Philip II was the youngest of nine siblings, six of whom reached adulthood. When he too died without male descendants in 1595, Philip II succeeded.
The couple took residence at the secularised monastery of Katlenburg, which Philip II had rebuilt in a Renaissance style.
In 1595 Duke Philipp II moved his residence from Katlenburg to Herzberg Castle. He reigned less than one year.
However, the Lüneburg branch of the Welf dynasty objected to the annexation and took the matter to the Reichskammergericht. In 1617, after a prolonged legal case, Henry Julius"s son Frederick Ulrich had to cede the former Principality of Grubenhagen to Duke Christian of Brunswick-Lüneburg.