From Kate's biography it looks like she is a commoner. Does this not negate William's chances of being King. Can Charles even become king being married to Camilla. I was under the impression that the princesses had to be of royal blood.
There is no stipulation that members of the royal family need marry other royals. When Prince William marries Kate Middleton it will have no effect whatsoever on his chances of becoming king. Prince Charles' position as second-in-line is also unaffected by his 2005 second marriage to Camilla Parker Bowles.
In Queen Victoria's day, at one point it was out of the question for members of the royal family to marry beneath their rank and station. If a royal did so they risked banishment. If they held military rank they could be stripped of that as well. Such marriages were called morganatic, whereby the lesser-ranking spouse and any children they may have, did not share the royal titles or any inheritances that go with it. However, the Queen was an ardent matchmaker and could turn a blind-eye to royal status when it suited her to do so.
One example of this is the marriage of Queen Mary and King George V. Queen Mary's (then Princess May of Teck) father was the product of a morganatic marriage. While both her parents held royal titles, Princess May was a mere Serene Highness as opposed to a Royal Highness, thus making her not royal enough to marry royalty, but too royal to marry a commoner. Queen Victoria bypassed this issue and allowed her to marry her grandson, the future King George V. Given that no one would think of Queen Mary as anything less than royal now, it's rather ironic that she wasn't considered royal enough at the time.
As royal houses fell during the First World War there was a shortage of eligible princes/princesses. For practical purposes royalty started looking towards the aristocracy for spouses. This is still an option however it seems as though members of the royal family are choosing to marry for love and compatibility as opposed to trying to make alliances between royal or aristocratic houses.
Like the Crown Princes of Denmark, the Netherlands, Norway, and even the Crown Princess of Sweden, Prince William has chosen a commoner for a spouse. And like them, his (and Prince Charles') position in line to the throne is completely unaffected by it.
© Marilyn Braun 2010