abstract:Mountbatten-Windsor is the personal surname of some of the descendants of Queen Elizabeth II and Prince Philip, Duke of Edinburgh under an Order in Council issued in 1960, which has not been applied consistently. While the Order specifically applies the surname "Mountbatten-Windsor" to those descendants of the Queen not holding Royal styles and titles, "Mountbatten-Windsor" has been formally used by some descendents of Queen Elizabeth II who do hold Royal styles.
The new baby will not be given the title of Her Royal Highness, but will instead be known as Lady (with the chosen Christian name) Windsor or possibly Mountbatten-Windsor.