Emmanuel Philibert was sent to Charles V in July 1545. In Brussels he has forged a strong bond with his first maternal cousin Philip of Spain and he was proclaimed lieutenant general in Flanders and supreme commander of the imperial armies (27 June 1553).
Dead his father, the duke Charles III, on the night between 16 and 17 August 1553 in Vercelli, there was remained almost nothing of the his State.
Convinced that only on the battlefield could find salvation of the Savoyard state, Emmanuel Philibert participated in the various military exploits of his uncle Emperor Charles V. However, were those years of needs and economic necessities almost humiliating, to which little could cope sacrificed the ducal finances. He was forced to restrict his personal expenses to a minimum and its already small court.
A year after his father's death, on 15 July 1554, Emmanuel Philibert was officially invested by Charles V of the Duchy of Savoy, an investiture only formal, since almost all of the Duchy in the hands of the French. The estates still in the hands of the Savoy were few and isolated from each other: Vercelli, Asti, Ceva, Fossano, Cuneo, Nice, Ivrea and the Val d'Aosta.
Three weeks later, at Arras, the new duke made his will. The indications were very precise and binding: the Emmanuel Philibert indicated his cousin Jacques, duke of Nemours, as the heir of all his states «provided that, however, he leaves the service of the king of France [...] and submit himself to the good graces of the Emperor, from which depend his states, and pay due obedience; if he does not fulfill the provisions above within a month, he [Jacques] will be private [of his inheritance and rights] and will be invested as heir Philip of Austria, son of the Emperor, Prince of Spain». Equally, if Jacques died without heirs, Philip would be the heir. This will clearly reveals the political and diplomatic pact there is under: in case of death of Emmanuel Philibert, Spain would have secured all the rights of succession on the Savoy state. Thus, Emmanuel Philibert linked the future of the house of Savoy exclusively to its military capabilities on the one hand, and to a future marriage, on the other.
Here, then, the importance of the marriage of Emmanuel Philibert.