The fief of Carignano had belonged to the Savoys since 1418, and the fact that it was part of Piedmont, only twenty km. south of Turin, meant that it could be a "princedom" for Thomas in name only, being endowed neither with independence nor revenues of substance. Instead of receiving a significant patrimony, Thomas was wed in 1625 to Marie de Bourbon; she was sister to and co-heiress with Louis, Count of Soissons, who would be killed in 1641 while fomenting rebellion against Cardinal Richelieu.