Charles, Germaine, and Charles's sister Eleanor moved from Castile to Aragon in 1519, where he would be formally sworn in as King of Aragon. He would spend a year in Aragon, negotiating with its parliament and managing affairs. While in Barcelona, Charles arranged for Germaine to marry the margrave Johann of Brandenburg-Ansbach, a landless cadet and cousin of Joachim I, Elector of Brandenburg. Germaine left Spain to travel with Charles to Germany, where she was married.
In 1523 Charles appointed the couple jointly viceroys of Valencia.
On Johann's death in 1526, Germaine married Ferdinand of Aragón, Duke of Calabria.