After Anushapati was assassinated in 1248, his son, Wishnuwardhana, became king of Singhasari. In 1254 King Wishnuwardhana appointed his son Kertanagara to rule at his side, probably to ease the transfer of power after his death. He died a natural death in 1268, and Kertanagara became the sole ruler.
See the family tree (pdf)
The Nagarakertagama informs us that Wishnuwardhana was deified in Waleri in the form of a Shiva image, and in Jajaghu in the form of a Sugata (Buddhist) image. Jajaghu has been identified as the temple now known as Jago, after the village where it is located (close to Malang).
Candi Jago was indeed a Buddhist temple. The main image in the temple was of Amoghapasha Lokeshvara, an eight-armed form of the Bodhisattva Avalokiteshvara. The image is still at the site. Unfortunately its head has been damaged.
The other images belonging to this temple are: Sudhanakumara, Shyamatara, Hayagriva and Bhrikuti, now in Jakarta, and the images of the Jina Buddhas and their female counterparts. Not all of these have survived. Some are in Jakarta and one is in the British Museum in London.