Complex sentence: As a tutor to Carlos I of Spain (afterwards Emperor Charles V), Guillaume became the power behind the Spanish throne during his pupil's minority, obtaining for himself the titles of Marquis of Aerschot and Duke of Soria and Archi.
Split into simpler sentences: As a tutor to Carlos I of Spain (afterwards emperor Charles V), Guillaume became the power behind the Spanish throne during his pupil's minority. Thus obtaining for himself the titles of Marquess of Aerschot and Duke of Soria and Archi.