Excellency
Honorific title used for high-ranking officials such as ambassadors, ministers, and governors. Can be used as a standalone noun or as a suffix after a name or title.
His Excellency the Ambassador will be attending.
His Excellency the Ambassador met with the President today.
閣下、どうぞこちらへ。
Your Excellency, please come this way.
殿下 addresses princes and princesses of royal blood, whereas 閣下 addresses appointed or elected high officials rather than royalty.
From Chinese 閣下, literally 'below the tower/pavilion', originally a respectful way to address a high official without using their name directly.