Artistic License Gone Wrong

I recently started a new commission for a friend who loves cats. I was so excited to create something special for them, but halfway through the project, I noticed that their cat had an unusual birthmark shaped like a tiny star on its ear. I incorporated this detail into my painting without telling my friend because it seemed unique and added character. Now I'm unsure if revealing this secret addition might seem presumptuous or intrusive since I didn't ask about it first. It's hard to know what to do when you're so eager to make someone happy but also want to stay true to the truth of their beloved pet.