Lady Dianna was chosen to bear an heir to the throne because the reptilian royal family had become too incestuous over the last century or so.
Queen Victoria married her first cousin Prince Albert in 1840.
Their grandson King George married his cousin princess Victoria in 1893, months after she was supposed to marry his big brother Albert who had been heir to the throne but had died.
More recently Queen Elizabeth married Prince Phillip of the Danish and Greek royal families. They are both great great grandchildren of Victoria and Albert. Charles needed a wife he was not too related to or else his kids could have become pure reptile.