Vhagar

Magister Illyrio Mopatis sent the Saduleon, Joso’s Prank and the Summer Sun to Qarth to bring Daenerys Targaryen back to Pentos in preparation for her return to Westeros. Daenerys accepted, but insisted in renaming the ships as Vhagar, Meraxes and Balerion, in homage of the three powerful dragons of Aegon the Conqueror which were in turn named after gods of Old Valyria.

Balerion is the great cog previously known as Saduleon; Meraxes is the galley previously known as Joso’s Prank; and by implication, Vhagar is the galley formerly named Summer Sun.