‘Yummy!’ thought the woodworms when they saw this painting. It was painted on a wooden plank (a panel). They ate up William of Orange’s left shoulder and arm. So the wood was replaced with a new piece a long time ago. The conservator painted his sleeve all over again on the new wood.
Luckily, Adriaen Key made several paintings of the prince that look just like this one. So the conservator could copy the sleeve, and she didn’t have to make it up herself. Although it might have been fun to paint it in some nice new colours.