Charles I, crowned king of England in 1625, was illegally executed on January 30, 1649, primarily for defending the Anglican Church. His body was secretly buried in Windsor Castle, and he was widely acclaimed as a martyr. A royal decree ordered a special service on this day to be in the Book of Common Prayer from 1662 to 1859. It also ordered it to be a day of national fasting. The anniversary of this event is commemorated by the Society of Charles the Martyr with an annual service at the site of his execution in Whitehall, London.
Source: The Free Dictionary