U.S. Secretary of State John Kerry assumed a royal prerogative Tuesday as he praised William Hague after his resignation as British foreign secretary, calling him "Sir William" in a Twitter message.

"Will miss working so closely with my friend Sir William -- when @WilliamJHague spoke, we all listened," Kerry said in a tweet on his page on the social media site, to which a photograph of the two men was attached.

Hague has not been knighted, an honor normally bestowed by the British monarch, Queen Elizabeth II, and which carries with it the title "Sir." It is an honor often given to statesmen, as well as other distinguished citizens from business leaders to entertainers.

Hague said on Monday he was stepping down from his post as Britain's top diplomat after four years in the job, an unexpected move prompted by a government reshuffle by Prime Minister David Cameron.

He will become leader of the House of Commons, coordinating the government's business in the lower house of Britain's parliament.

Earlier, the U.S. State Department spokeswoman, Jen Psaki, said the "excellent working relationship" Kerry had with Hague "exemplified the U.S.-U.K. special relationship."

Britain was the first country Kerry visited when he became secretary of state last year and Hague was the first foreign minister to receive him.

Psaki said the United States believed relations with Britain would remain equally strong under Hague's successor, Philip Hammond, the former defense minister and a prominent Euro skeptic.

Psaki avoided being drawn when asked if the United States was concerned about Hammond's outspoken criticism of the European Union, a 28-nation grouping Washington supports as an entity.

"I think we'll leave that to domestic politics in the U.K," she said.