How can I open the locked door?

Hint 1 of 14:

You cannot go back through the King's Throne Room, but you can enter his
bedroom.

Hint 2 of 14:

The door is locked, however.

Hint 3 of 14:

You can't bother the king anymore, but you can bother his servants.

Hint 4 of 14:

Someone he might trust.

Hint 5 of 14:

Somebody who might be of the utmost protective nature.

Hint 6 of 14:

Somebody whom the king trusts enough, that he would give him/her the key to
all of his personal possessions.

Hint 7 of 14:

One of the guards in the front of the castle holds the key.

Hint 8 of 14:

You have to figure out how to get the guard to "give" you the key.

Hint 9 of 14:

Maybe "give" might have not been the right word.