Battle of Chernomorets

When Michael Shishman ascended the Bulgarian throne in the spring of 1323, the country faced substantial losses of its possessions south of the Balkan Mountains. The new Bulgarian ruler therefore hurried to move his troops into Thrace and begin a campaign to recover the captured Bulgarian towns. As the Byzantine forces were concentrated around Plovdiv, Michael Shishman made the acquisition of lands in southeastern Thrace the objective of his campaign. Following a successful campaign, all the territories except Plovdiv were liberated. 

A few years later, during another Byzantine civil war, fought between the "old emperor" Andronikos II and his grandson Andronikos III, the Bulgarian tsar decided to intervene and take sides in the conflict. He chose to support the younger claimant, Andronikos III, despite their previous hostility on the battlefield. In May 1327, the two rulers, the Bulgarian tsar and the younger claimant Andronikos III, met near the town of Chernomen.

After eight days of negotiations, the parties signed a peace treaty recognising Bulgarian authority over the lands between Sliven and Mesembria. The treaty provided for the marriage of Michael Shishman to the former wife of the previous tsar Theodore Svetoslav, Theodora Palaiologina. Theodora Palaiologina was the sister of Andronikos III, which was strategically important for strengthening relations between Bulgaria and Byzantium.