Ivan Dmitrievich (1380 , Moscow - July 29, 1393, Moscow) - prince, son of Dmitry Donskoy . He died by taking monastic vows with the name of Joasaph.
Presumably, it was his grave that was found during the repair of the porch of the Cathedral of the Savior in the forest in 1836, when two burial places were found in stone coffins typical of the 14th century - wide at the head and tapering to the feet. In one of these coffins there was a well-preserved burial of a man in a monastic robes, which supposedly belonged to Ivan Dmitrievich. 
After the demolition of the cathedral in 1933, the grave was lost.