We have a matching set of Carsland/Goofy hats that my hubby is mostly too embarrassed to wear. Haha, but maybe your partner will be more accommodating!! There are a lot of character based designs, too, so maybe you could match some movie characters? Or Chip and Dale!! Or Vader and Leia! I know there are Princess themes, but I just don't know if I've ever seen a Prince/King theme. Have fun!!
They have had in the past "I'm his Beauty" "I'm her Beast" tshirts that coordinated too if you just want something that matches. There are about a million similar designs on Etsy too, some come on shirts so you print at home and iron on to your own shirts.