Towards the end of 1550, Knox was appointed a preacher of St Nicholas' Church in Newcastle upon Tyne. The following year he was appointed one of the six royal chaplains serving the King. On 16 October 1551, John Dudley, 1st Duke of Northumberland, overthrew the Duke of Somerset to become the new regent of the young King. Knox condemned the "coup d'état" in a sermon on All Saints Day. When Dudley visited Newcastle and listened to his preaching in June 1552, he had mixed feelings about the fire-brand preacher, but he saw Knox as a potential asset. Knox was asked to come to London to preach before the Court. In his first sermon, he advocated a change for the second edition of the "Book of Common Prayer". The liturgy required worshippers to kneel during communion. Knox and the other chaplains considered this to be idolatry. It triggered a debate where Archbishop Cranmer was called upon to defend the practice. The end result was a compromise in which the famous Black Rubric, which declared that no adoration is intended while kneeling, was included in the second edition.