The newborn will be actually be seventh in the British royal family order of succession. The basis for the line to the throne was determined all the way back in the constitutional developments of the seventeenth century, in the 1689 Bill of Rights and the 1701 Act of Settlement.
Of course, the succession to the throne is also regulated not only through descent, but also by the Parliament -- a royal can be deprived of his or her title through misgovernment.
Harry and Meghan's baby will fall directly behind Harry in line to the throne, and also behind Prince William and Kate Middleton's three children -- 5-year-old Prince George, 4-year-old Princess Charlotte and 1-year-old Prince Louis -- who take up the third, fourth and fifth spots, respectively. Interestingly, in 2013, a new act was passed decreeing that male heirs no longer take precedence over their sisters, which is why Princess Charlotte is ahead of Prince Louis.
Meanwhile, Prince Charles remains at the top spot to succeed his mother, Queen Elizabeth II, followed by Prince William.
Baby Sussex, whose name has yet to be revealed, does, however, knock Prince Andrew, The Duke of York, as well as his daughters -- Princess Beatrice and Princess Eugenie -- one spot down. Prince Andrew will now occupy the eighth spot, while Beatrice and Eugenie will take the ninth and 10th spots.