Prince of Llamedos
The courtesy title for the eldest son of the King of Ankh. This no doubt stems from a time when Llamedos was a tributary part of the Ankh-Morporkian Empire. The Llamedosians, in all probability, have never really accepted this, and reaction to being a Principality has ranged over the years from dissent expressed as armed revolution, right down to the most-recently-expressed laid back attitude of "well, if makes you happy to call yourself that, boyo, no skin off our nose, is it?" . This was usually accompanied by behind-the-hands sniggering at the terrible mess the Prince made of speaking Llamedosian, although the fact he even bothered to attempt learning the llanguage usually won him a few brownie points.
While all this has fallen into abeyance since the death of the last King and the re-assertion of independence by the Llamedosians, it is interesting to reflect that Carrot Ironfoundersson, by virtue of being (uncrowned) heir to the throne of Ankh-Morpork, and childless, is also, de facto, Prince of Llamedos.
Annotation
Llamedos is the Discworld incarnation of the Roundworld principality of Wales. One of the hereditary titles of the heir to the British throne is Prince of Wales. Prince Charles was the postholder throughout the majority of Sir Terry's life. Prior to Charles' investiture at Caernarfon Castle (1969) he was a student at Aberystwyth University, where he learnt to speak a slightly strained and idiosyncratic kind of Welsh. While some unkind people sniggered, it is safe to say that most of the Welsh felt the gesture deserved an appreciative nod and a couple of judges' scorecards holding up at least an "eight".