Jovan Uros Nemanjic Palaeologus (monastic name Joasaf) was born in Thessaly in 1350. His mother was a Byzantine princess, Maria Palaeologus, a nice of Byzantine emperor Andronicus II Palaeologus, while his father Sinisa Uros Nemanjic was a step brother of the Serbian ruler Stefan Dusan the Mighty. Sinisa was the ruler of Epirus and Thessaly, who were the part of the Serbian state, or at least in the vassal status with Serbia throughout the great part of 13th nd 14th century.

His inheritor Jovan Uros was more interested in Church, the saints and spiritual things than in regency, the same way as his ancestors were. After the death of Jovan's father in 1371, he was declared a Despot of Epirous and Thessaly and than arrived to Trikala. Then he meets the monk Athanasios of Meteor, the founder and the abbot of the monastery Grand Meteora. Athanasios becomes his spiritual father and a role model. Young Despot hands over the administration of his province to his cousin Alexy Angel Filantropin and in the monastery Grand Meteora becomes a monk named Joasaf. Monastic life wasn't hard for him. He was fulfilling all the commitments assigned with, he respected the Kinovium (a set of rules about behavior in the monastery and community) and very soon he gained the respect of the elders and other monks. Since he was a very rich man, he was very generously donating churches and monasteries, either on the Holy Mountain, or in the Meteora community. Saint Joasaf was fresco-painted along with Athanasios of Meteor as the second founder of the Grand Meteora monastery. He has built a several monk cells, the monastery hospital, the tank system for collecting the rainwater, and he renewed the nets and ropes system for delivering goods, and also established the contact with the outside world.

Athanasios of Meteor declared Joasaf his inheritor as the abbot of the Grand Meteora monastery.

Joasaf died in peace and prayer, in a small and humble monk cell, and his relics are nowadays kept in the Grand Meteora monastery. Saint Joasaf was the last male descendant of Nemanjic dynasty.