Through the intervention of his aunt, Richlind of Altdorf, he also inherited the property of her late husband Count Adalbero II of Ebersberg in 1045.

[4] Together with Duke Bretislaus I of Bohemia, Welf accompanied Emperor Henry III on his 1051 campaign against King Andrew I of Hungary.

[5] Later however, he turned against the emperor and got involved in a conspiracy around the deposed Duke Conrad I of Bavaria, who with Hungarian support raided the Carinthian March of Styria.

Welf III never married and had no children when he died at his castle in Bodman on Lake Constance on 13 November 1055.

In 1057 Emperor Henry's widow Agnes of Poitou ceded the Carinthian duchy to the Ezzonid scion Conrad III.