Britains royal palace said Friday that the infant son of the Duke and Duchess of Cambridge has been named Louis Arthur Charles. The palace said that the babys full title is His Royal Highness Prince Louis of Cambridge. Louis is Williams fourth name as well as being that of Earl Mountbatten, to whom Williams father Prince Charles was particularly close. Mountbatten was the uncle of Prince Philip, 96, great-grandfather of the new prince. William and Kates third child was born Monday, a brother to 4-year-old Prince George and Princess Charlotte, who is almost 3. Louis is fifth in line to the throne after his grandfather Prince Charles, his father and older siblings. Charles has said it was a great joy to have another grandchild.