I believe there have been several studies on this situation, when it happened accidentally, and I wonder if you are referring to one of these. Below are some articles that discuss the outcomes of twins who were separated at birth.
Shirley Cress Dudley, MA LPC
Founder of The Blended and Step Family Resource Center
Blended Family Just Ask Expert
Interesting question! I would imagine that the two would be happy to be reunited, and once the excitement starting wearing thin, I would expect them to have resentment toward the parents.
You mentioned that they were separated by divorce, well, I would think that they would wonder how it was decided for which to live with whom and would have feelings of abandonment by the other parent.
I also wonder if it would make them question their individual identity, are they so much alike that they are that easily misplaced, that one would compensate for the feelings of love for the other or if they could be replaced that simply.
I feel that there would be mental stress and disappointment and you mention that they meet in their early teens, when children are already struggling with their identity and other issues, this might would complicate an already complicated time.
It sounds like a very sad situation to me, but in the end, I feel as though the parents will be the ones to suffer the greater loss.