He had a son, Bernard III, and a daughter, Stephanie, who married Count Roger II of Foix.
[4] To seal the new alliance between Besalú and Barcelona, William agreed to marry Raymond Berengar's sister-in-law, Llúcia, daughter of Count Bernard I of La Marche.
On 11 December 1054, William signed a scriptura dotis, a charter granting a dower to Llúcia.
In accordance with the Liber iudiciorum, the Visigothic law still in effect in Catalonia, he granted Llúcia one tenth of all his possessions.
That same day he also made what he called a scriptura donationis causa sponsalitii, a donation on the occasion of his betrothal, granting Llúcia the counties of Berga and Ripoll and all that pertained to them.