Not the first

The princess locked the door to the bathroom, not aware of what was happening outside of her chambers.

Things were brewing, and she was unaware.

She was planning on what to do the next day since her brother isn't back from the mountains, and there was no way for her to take the boy to the dad.

Osy has made it pretty clear he won't see them should they try to bother him.

The assassin made sure there was no one around before he slipped into the princess's room.

They didn't need to bother with the lock. It was easy for the assassin to go through locked doors, although it doesn't last for long.

The assassin only needed to go through a door four times. And thereafter, they won't be able to go through the door, even if they want to do that.

The assassin walked into the visiting room. They didn't waste time there, as they headed straight to the private chambers.