Originally Posted by pacanis
When I first started watching it I thought Robert and his immediate family's last names was Grantham, while the cousins' (Matthew and Isobel) names were Crawley. Then I caught that his last name was Crawley, too, and couldn't figure where Grantham came from.
Remember when Princess Margaret wanted to marry Anthony Armstong-Jones? Well, her sister, the Queen, didn't want her sister's children to be born commoners. So she bestowed the title of "Earl of Snowdon" upon her husband-to-be just prior to the marriage. So now the family name is Armstrong-Jones, House of Snowdon. The family lineage is passed down through the male heirs. Unless there are no male heirs, until recently with the birth of Prince William's child, should it be a girl.
"Earl of Snowdon" is one of those titles that petered out due to no male heirs to carry it on. So the Queen resurrected it for Anthony. Just like the "Duchess of Cambridge" for Prince William's wife. To have a child of William's be entitled to the throne without a Title from both parents would have made the child half-commoner. And you certainly don't want just any commoner taking control of the throne.
Princess Anne, chose to not have a title bestowed upon her husband. Thus her children, granchildren to the Queen, have no title either, nor can they claim one without the Queen's permission or her bestowing one upon them. Thus they are considered commoners. And waaaay down the line of inheritence to the throne. And of all the immediate family members that make appearances on behalf of "The Firm", Princess Anne makes the most.
So there is your mini history lesson on The Royal Family of England.