Henry concluded a truce with Laskaris in July 1207. He also had a meeting with Boniface of Thessalonica, who acknowledged his suzerainty at Kypsela in Thrace. However, on his way back to Thessalonica, Boniface was ambushed and killed at Mosynopolis on 4September. According to Geoffrey of Villehardouin local Bulgarians were the perpetrators and they sent Boniface's head to Kaloyan. Robert of Clari and Choniates recorded that Kaloyan had set up the ambush. Boniface was succeeded by his minor son, Demetrius. The child king's mother, Margaret of Hungary, took up the administration of the kingdom. Kaloyan hurried to Thessalonica and laid siege to the town.