[1] His tenure was marked by a violent conflict with the Latin Archbishop of Patras, William Frangipani.
When William died in 1337, Bertrand laid siege to Patras hoping to reduce it to obedience before the arrival of his successor, Roger.
Pope Benedict XII reacted by declaring the city "land of the Holy Roman Church" and placed the Principality under the interdict.
As a result, Bertrand had to retreat, and the Archbishop became independent, although his secular fiefs still owed allegiance and services to the Prince.
[4][5] He then returned to France, where in 1345 Pope Clement VI appointed him to replace Martino Zaccaria and the other leaders of the Smyrniote Crusade after they were killed in an ambush.