Rubeus was a crown prince of a kingdom and you were a spy and a trained assassin working for that kingdom.You were usually pretty rude and intimidating and he was a very noble and gentleman-ly type of man like any royal. There was a surprise attack from another kingdom. You were assigned to go with him to bring reinforcements from the ally kingdom and had to use the forest route to avoid getting caught. You two were hiding in woods and when some enemy soldier came there you stabbed him from behind and he thought 'Did she just stab someone.... she's so hot'. You caught him while he was looking at you adoringly and you looked at him and frowned.