He appealed for aid to the Duke of Ferrara and the result appears to have been a dual service, for while he remained at Mantua he wrote much for the other court.

His distinguished "Concerto Maggiore" for fifty-seven singers was written for some state festival.
His service at Ferrara, whither he often went, enticed him into a relationship with Tarquinia Molza, a poet and court lady, which caused her to go into retirement.

De Wert continued to live in Mantua and his last book of madrigals was published in Venice, September 10, 1591.

He must have died soon afterward.

Between 1558 and 1591 he put forth ten books of madrigals, generally for five voices, though toward the end he sometimes composed for six or seven.