Pierre Duparc [fr] mentions the hypothesis of Jules Vuy, who believed that the new count took office at some time before the death of Amadeus.
A transaction is set up between the two parties, on May 29, 1308, by the executor, Jean I of Chalon-Arlay, brother of Agnes, and under the auspices of the Bishop of Geneva.
Three years later, a new transaction was established in favor of the count by Jean de Chalon and reducing the share of inheritance of his mother, forcing her to renounce all claims on the county.
This act is guaranteed in February in particular by the Dauphin John II of Viennois, the son of the count Savoy Edward and Guichard VI de Beaujeu.
At the peace treaty between the Count of Savoy and the Great Dauphine Béatrice of August 1308, William "vouches for its execution".
He also ratified past agreements, including the peace of Annemasse from 1287 or the arbitral award of 1293 passed with William, bishop of Lausanne, and Aimon of Quart [fr].
Finally, on January 21, 1312, the sons of the count of Savoy, Édouard and Aymon, signed an agreement committing the various parties to divide the barony of Faucigny, in case of death without heir of Lord Hugues.
He also paid tribute to the Dauphin of Viennois, recognizing holding in fief his county and various castles of this lord, June 13, 1316.