Aye, this is true. Hmm, I do wonder if this exact scenario would play out with other sons of James II and Anne Hyde also.
Charles would be 25 when his father ascends the throne, and 28 in 1688, he'd have his own power base I think, or his own supporters at least, I definitely think there'd be people plotting to see him on the throne without civil war. And I can see James being slightly paranoid about that.
Would James II consider remarrying if he has say three sons surviving from his marriage with Anne?