With the help of his cousin Otto of Brunswick-Grubenhagen, John turned against the Angevins of Naples, who had large possessions in Piedmont and Savoy.
In 1343, when Robert, King of Naples died and his young granddaughter Joanna I took the crown, John took the opportunity to expand his control in northern Italy.
[2] With the tacit support of Luchino Visconti, John occupied Alba, Bra, Valenza and, in 1348, Cuneo.
By a marriage to the last titular Queen of Majorca, Isabella,[3] he lost the support of the emperor and had to fend off attacks from imperial and Visconti troops.
He had four sons, three of whom succeeded him in turn, and a daughter with his wife Isabella (Secondotto, John III, Theodore II, Margaret and William).