Passage: In the 15th century, the grand princes of Moscow continued to consolidate Russian land to increase their population and wealth. The most successful practitioner of this process was Ivan III, who laid the foundations for a Russian national state. Ivan competed with his powerful northwestern rival, the Grand Duchy of Lithuania, for control over some of the semi-independent Upper Principalities in the upper Dnieper and Oka River basins.Through the defections of some princes, border skirmishes, and a long war with the Novgorod Republic, Ivan III was able to annex Novgorod and Tver. As a result, the Grand Duchy of Moscow tripled in size under his rule. During his conflict with Pskov, a monk named Filofei (Philotheus of Pskov) composed a letter to Ivan III, with the prophecy that the latter's kingdom would be the Third Rome. The Fall of Constantinople and the death of the last Greek Orthodox Christian emperor contributed to this new idea of Moscow as 'New Rome' and the seat of Orthodox Christianity.

Question: Who was the monk that wrote Ivan III a letter?
Filofei