Saint Euphrosyne, in the world Eudocia, was the daughter of the Suzdal prince Demetrius Constantovich (+ 1383), and from 1367 was the wife of the Moscow Great Prince Demetrius of the Don. Their happy union was for Russia a pledge of unity and peace between Moscow and Suzdal.

Saint Alexis, Metropolitan of Moscow, and even Saint Sergius of Radonezh, who baptized one of the sons of Demetrius and Eudocia, had a great influence upon the spiritual life of Princess Eudocia. Saint Demetrius of Priluki (February 11) was the godfather of another son.

The holy princess was a builder of churches. In 1387 she founded the Ascension women’s monastery in the Moscow Kremlin. In 1395, during Tamerlane’s invasion into the southern regions of Russia, the Vladimir Icon of the Mother of God was transferred to Moscow upon her advice, miraculously defending the Russian land. During Lent, the princess secretly wore chains beneath her splendid royal garb. By her patronage the famous icon of the Archangel Michael was painted, and later became the patronal icon of the Kremlin’s Archangel Cathedral.

After raising five sons (a sixth died in infancy), the princess was tonsured as a nun with the name Euphrosyne. She completed her earthly journey on July 7, 1407 and was buried in the Ascension monastery she founded.

An old Russian church poem has survived, the lament of the princess for her husband, who had died at the age of thirty-nine.

Saint Euphrosyne is also commemorated on July 7.

Source:

https://oca.org/saints/lives/2017/05/17/101407-st-euphrosyne-the-princess-eudocia-of-moscow