Julian thought he was so lucky that the rash didn't show immediately, so the king and queen didn't see it. They said Liam loved oysters. That meant he must not have the allergy that Julian had. If they saw him with his rash right after eating oysters, it's impossible they didn't suspect him.
The king and queen must have already thought something was off with their 'son' but they just brush it off because what were the odds that their only son would have a doppelganger? It was unheard of.
Right.
Julian must immediately find a way to get out of the palace before his disguise was blown. The young man decided to approach the window to check his surroundings. What he saw made him grit his teeth.
There were several soldiers who walked back and forth through the royal palace's grounds, the entire place was very secure from would-be thieves, or in Julian's case, someone who wanted to get out.