Passage: Mevlâna's successor Hüsamettin Çelebi decided to build a mausoleum (Kubbe-i-Hadra) over the grave of his master. The Seljuk construction, under architect Badr al-Din Tabrizi, was finished in 1274. Gürcü Hatun, the wife of the Seljuk Emir Suleyman Pervane, and Emir Alameddin Kayser funded the construction. The cylindrical drum of the dome originally rested on four pillars. The conical dome is covered with turquoise faience.

Question: Who was Mevlana's successor?
Hüsamettin Çelebi