The Monday after Pentecost, added to the calendar by Pope Francis in 2018. Mother of the Church (Latin: Mater Ecclesiae) is a title given to Mary in the Catholic Church, as officially declared by Pope Paul VI in 1964. The title first appeared in the 4th century writings of Saint Ambrose of Milan, as rediscovered by Hugo Rahner. It was also used by Pope Benedict XIV in 1748 and then by Pope Leo XIII in 1885. Pope John Paul II placed it in the Catechism of the Catholic Church, and Pope Francis inserted a memorial with the title "Mary, Mother of the Church" into the Roman Calendar, celebrated annually on Whit Monday, the day after Pentecost. Wiki link Dates computed from the General Roman Calendar. Text: Wikipedia (CC BY-SA).