While working on an article about Jean Plaidy (yay! finished), I had cause to look at some of my old Fawcett editions of Plaidy, and I suddenly realized something (OK, it's hot here, and I'm a bit slow): the covers of The Queen From Provence, Hammer of the Scots, and The Vow on the Heron all used the same model for the king. He's doing different things on each cover, of course--preparing to smooch a gorgeous blonde on a white horse in The Queen From Provence, nibbling the ear of a fiery brunette on Hammer of the Scots, and angling for a kiss from a blonde with a Farrah Fawcett hairdo while standing aboard a ship on The Vow on the Heron--but it's definitely the same chap, with crisply curling blondish brown hair and a little moustache. On Hammer of the Scots, he has a short beard. He's wearing the same crown on all three covers.
Sadly, my digital photography skills haven't yet allowed me to get a nice close-up, but until I do, you may be able to get a hint from these covers: