crown prince 
noun
(In some countries) a male heir to a throne.But even though it was Vicant that was Crown prince and heir to the throne, it was Torrine who held their respect....
- Queen Victoria intended her to marry the British Crown prince, who was reportedly very pleased with the prospect.
- You're the Crown prince of an Empire so far ahead of us I suspect you could wipe out the entire kingdom with what you've got here!