I too had an adoptee of King Robert's as the heir apparent, and a disloyal one at that too, but he got killed in the Middle East (sort of on purpose - I'd reluctantly accepted him by now, as he was improving too, but still...). The real annoying thingy here is the fact that after his demise, the title of Crown Prince went not to Henry, third son of William and brother of the King, but to a guy he had adopted some time before!
So, instead of the crown passing to the King's brother in the absence of any royal offspring, it will pass to the brother's eldest son, who isn't even related to them. He showed some promise too, so it's a pity he'll have to go...