A German captain called Warner, who had deserted the Hungarian army to sell himself to the queen, had again played the traitor and sold himself once more, allowed himself to be surprised at Corneto by Conrad Lupo, the King of Hungary's vicar-general, and openly joined him, taking along with him a great party of the adventurers who fought under his orders.

This unexpected defection forced Louis of Tarentum to retire to Naples.

The King of Hungary soon learning that the troops had rallied round his banner, and only awaited his return to march upon the capital, disembarked with a strong reinforcement of cavalry at the port of Manfredonia, and taking Trani, Canosa, and Salerno, went forward to lay siege to Aversa.
The news fell like a thunder-clap on Joan and her husband.

The Hungarian army consisted of 10,000 horse and more than 7000 infantry, and Aversa had only 500 soldiers under Giacomo Pignatelli.

In spite of the immense disproportion of the numbers, the Neapolitan general vigorously repelled the attack; and the King of Hungary, fighting in the front, was wounded in his foot by an arrow.