Ban Ki-moon has joked to hundreds of diplomats and U.N. staff as he left United Nations headquarters for the last time as secretary-general that he feels like Cinderella because everything changes for him at midnight on New Year's Eve.

Flanked by the presidents of the General Assembly and the Security Council, the native South Korean thanked U.N. workers Friday for their hard work and commitment during his 10-year tenure that ends at midnight Dec. 31.

He told his colleagues he had two words for them: "Thank You."

As the top U.N. official over the last decade, Ban fostered a global agreement to combat climate change and new U.N. goals to fight poverty and inequality. But he leaves amid continuing conflicts from Syria and Yemen to South Sudan and Libya.