 Fruzhin, the son of Tsar Ivan Shishman, and his cousin Konstantin, the heir of Ivan Sratsimir, who had emigrated to Hungary and Serbia as the Ottomans subjugated the Balkans, organized an uprising in northern Bulgaria aided by Wallachian ruler Mircea the Elder, Serbian despot Stefan Lazarević and Hungarian monarch Sigismund.The Ottoman defeat by Timur in the Battle of Ankara of 1402 provided good conditions for an uprising, and the Christian forces crossed the Danube from the north into the Bulgarian lands