Prince of Spain - unless you're letting Carlos Clemente survive, and him being more his grandfather's grandson than his parents' son, (not impossible, since Carlos was born in 1771, so he'd be 18 by the time grandpa kicks, as opposed to his younger brothers, born in 1780, 1783 and 1784 who were still in single digits) - is out.
Most likely match is the Neapolitan crown prince or an Austrian archduke
Could Carlos Clemente continue the good work of his grandfather?