Barbara Blomberg was the mother of Don John of Austria. Blomberg was born in Ratisbon (modern Germany), the eldest daughter of Wolfgang Plumberger or Blomberg, a burgher, and of his wife Sibilla Lohman. A singer, in 1546 she was for a short time the mistress of the Holy Roman Emperor Charles V, who was in Regensburg for the meeting of the Imperial Diet. On 24 February 1547 Blomberg gave birth to John of Austria, who was almost immediately taken from her and sent to be raised in Spain.

Shortly afterwards Blomberg married Hieronymus Kegel, an imperial official. In 1551 she moved to Brussels with her husband where Kegel was responsible for the equipment of the imperial mercenary army. They had three children.

When Kegel died in 1569, Blomberg and her children were in reduced financial circumstances. At the request of the governor of the Netherlands, the Duke of Alba, she was granted a pension by King Philip II of Spain.