Yes

Kept secret to your mother but not your half-sister, just above your vagina where your urethra should be is a second opening that when you need to pee or are aroused opens to release a 10 inch long dragon-like penis. You are a hermaphrodite

Your sister had found this out early on when she accidentally stimulated you measuring around your tail to make custom undergarments. Before then, you didn't know that girls didn't have an extendable pee tube (as you thought of it) or that it could become long hard and stiff. You both became very embarrassed after your sister explained that it wasn't normal, even more so when she showed you what a real girl (you were young at the time) had instead and your pee tube got even longer and harder, standing erect, pulling a small sack out below it.

Now that your gender is covered and you flashed back to a really embarrassing time what do you do?

You are standing just outside the castle you have lived in your whole life with your mother and half-sister behind the walls, clad in miss matched adapted armour and with a sword, shield and spear.