Sometime in 1547, Sigismund Augustus and Barbara wed in secret. Neither exact date nor circumstances are known. The Lithuanian Chronicles recorded the doubtful claim that Sigismund Augustus was forced into the marriage when he was caught with Barbara by the Radziwiłł cousins. According to research by Władysław Pociecha, the wedding probably took place between 26 July and 6 August. Her cousin Mikołaj "the Black" Radziwiłł was sent to Kraków to inform the Polish court that Sigismund Augustus and Barbara were married since 25 November 1545. It seems he failed the assignment and Sigismund Augustus had to travel to Poland himself. He departed Vilnius on 15 November; Barbara was sent to the Radziwiłł estate in Dubingiai. In a letter dated 20 November, courtier Stanisław Dowojno, starosta of Merkinė, informed Sigismund Augustus that due to the difficult journey Barbara had a miscarriage. If that indeed was true, and not an elaborate intrigue by the Radziwiłłs, it would explain the secret marriage – an attempt to provide legitimacy to the child. Another explanation could be that the bleeding was caused by a rupture of an internal abscess, an early sign of her terminal illness.