He later reached the apex of his power when he became the new vizier of the Sultanate of Rum, and its de facto ruler for a short period after Kaykhusraw's death.
Following their defeat at the Battle of Köse Dağ, the Seljuks sent a diplomatic mission headed by Shams al-Din Isfahani, the deputy (na'eb) of Kaykhusraw II and the commander-in-chief of the Sultanate's army, to the Mongol ruler Batu Khan.
[1] Eventually, Batu allowed Kaykhusraw II to stay in "power" as a subject ruler of the Mongols in return for a significant annual tribute.
[1] According to Andrew Peacock: "henceforth the Saljuq sultans were to play a secondary political role, pawns of the officials appointed by competing Mongol factions".
[2] Things were going well for Isfahani, until Mongol ruler Güyük Khan (r. 1246-1248) decided to confirm Kaykhusraw's second son, known regnally as Kilij Arslan IV, as the new sultan.