Ferrante began to spy on Pier Luigi and sent reports continually to Madrid. Pier Luigi did not remain passive; on 4 June 1547 he arranged the marriage of his daughter, Vittoria, with Guidobaldo II della Rovere, the Duke of Urbino. He also continued to work hard on the fortifications of his lands. Charles, concerned about the progress of work in Parma, was persuaded to give free rein to Ferrante to organize a conspiracy against the duke. Marquis Pallavicini Cortemaggiore offered support; but Ferrante preferred to rely on his distant kinsman Louis Gonzaga, Lord of Castiglione, and his brother Count Giovanni Anguissola, governor of Como. Anguissola was able to convince Count Agostino Landi, Marquis Giovan Luigi Confalonieri, and Girolamo Alessandro Pallavicini to join him. After Anguissola and others had stabbed him to death, the conspirators hung his body from a window of his palace in Piacenza. Charles V's vicar Ferrante Gonzaga captured the Duchy soon after, although subsequent events led to the return of the duchy to Pier-Luigi's son, Ottavio in 1551.