In February-March 1648, as a result of negotiations between Hetman Bohdan Khmelnytsky and the Crimean Khan İslâm III Giray and the conclusion of an agreement on a joint struggle against the Polish–Lithuanian Commonwealth, Tymish was left hostage in Bakhchisarai.

After the capture of the capital of the Moldavian principality by Iasi, the Ukrainian-Moldavian alliance was concluded, for the strengthening of which Tymish married the daughter of the Moldavan Prince Vasile Lupu - Ruxandra.

The alliance of Ukraine with the Principality of Moldavia caused concern among the Transylvanian Prince George II Rákóczi and the Wallachian lord Matei Besarab, who, uniting with the detachments of the candidate for the Moldavian throne of Chancellor (logofet) Gheorghe Ștefan, started a war against Lupul.

Trying to help his father-in-law, whose troops were surrounded by joint Wallachian-Polish forces in the Suceava Fortress (now Romania), Tymish, led by a 9,000-strong Cossack detachment, broke into the city on August 10.

In the first decade of August, Hetman Bohdan sent a new Cossack corps to the Principality of Moldavia, led by his eldest son and son-in-law Vasily Lupu, Timosh Khmelnytsky.

This attempt completely failed, because in the few days that passed from the arrival to Suceava, the Cossacks were able to build strong fortifications; the siege of the fortress began.

However, having only 10,000 soldiers in Chyhyryn (other regiments gathered near Bila Tserkva), he did not dare to send large forces to Suceava before the threat of an attack by the Poles (several thousand Cossacks could not save the situation).

Although the next night they tried to destroy the blockhouse in front of the Polish trenches, and almost succeeded in attacking it suddenly in the dark, the defenders were able to hold out (including hand grenades) to the approach of their cavalry, which drove the Cossacks to their camp.