Elisa, the daughter of Prince Antoni Radziwiłł and his wife, Princess Louise of Prussia, niece of King Frederick the Great and a relative of the Prussian Royal Family, was born in Berlin.

Another factor was the influence of the Mecklenburg kinsmen of the deceased Queen Louise in the German and Russian courts who were not fond of Radziwiłł's father and opposed the possible marriage.

Eventually, William asked for the hand of Augusta of Saxe-Weimar, fourteen years his junior, in marriage on 29 August 1826 (in writing and through the intervention of his father).

Historian Karin Feuerstein-Prasser has pointed out, on the basis of evaluations of the correspondence between both fiancées, the different expectations Wilhelm had of both marriages: he wrote to his sister, Czarina Alexandra Feodorovna (Charlotte of Prussia), wife of Czar Nicholas I of Russia, regarding Radziwiłł, that "One can love only once in life, really", but confessed regarding Augusta that "the princess is nice and clever, but she leaves me cold."

Though Augusta was in love with her future husband and hoped for a happy marriage, theirs was a troubled relationship; Radziwiłł was aware of this, and she believed that she herself would have been a better wife to the Prussian prince.