Prince Kistrin was neither fat nor ugly, but he was far from Vilgefortz's and Geralt's looks. The former was Olivia's teacher in her childhood. The latter was her foster father in her adolescence. Anyhow, regarding looks, he had already lost.
If Prince Kistrin was a character in a novel, then he would be nothing but a cameo. Unless the Gods granted him a "golden finger" and allowed him to transform from a side-character to a protagonist, one step at a time, he would amount to no more than a cameo.
Even so, as the heir to the Kingdom of Verden, he was far more talented than his cowardly, weak father. This prince was known for his great courage and valiance.
Of course, all this paled in comparison to his status as a once-fiancé of the "Pearl of the Northern Kingdoms." He had earned the envy of many bachelor aristocrats from all over the Northern Kingdoms.