Prince of Persia/WMG
It's very possible that the original Prince could be the father of the Sands of Time Prince, while the New Prince could be a distant cousin.
- Alternately, the new prince could be the first of the line of action-guy Persian princes. He may be a random tomb robber now, but he has just become very friendly with a real live princess. If they get married, he will become a prince, and his male descendants will be princes also.
We've been going backwards through the series
The 2008 Prince is the first one, he marries Elika and they have a child, the child is either the Sands of Time Prince or his father. Then The SOT Prince has a son, the Classic Prince.