Apart from the striking similarity of their appearance, the two men are not at all cut from the same cloth. Although the king is not a developed character in this story, the reader can deduce that he is a man preoccupied with the affairs of state more than those of his own household. His wife is not particularly close to her husband and immediately senses the difference when Russendyll comes on the scene. Russendyll, without abusing his conjugal privilege (since he is an imposter after all, even if it is for a good cause), is attentive and caring towards his "wife," unlike the king. In other words, Russendyll is better than the real thing!
At the end of the story when Russendyll helps see to it that the king is restored to his throne, it is with a certain bittersweet regret, but not from misplaced ambition. He renounces what is not his to have, and the most difficult part is to relinquish the queen's apparent love for him. He puts duty before his own feelings and acts as an honest man.
Russyndyll shows that he is truly noble of heart, and the reader can't help but wonder if the king himself could make such a claim.