Washington (CNN) -- Former Secretary of State Henry Kissinger used a short speech at the State Department on Wednesday to joke about the prospect of Hillary Clinton running for President in 2016.
Standing on stage with five other former or current secretaries of state, Kissinger -- who served as secretary of state under Presidents Richard Nixon and Gerald Ford -- highlighted the work of diplomats and foreign service officers as he spoke at the groundbreaking for the United States Diplomacy Center, a museum set to honor diplomatic work.
He then, however, dropped a slight joke about the prospect of Clinton running for president.
"We all know that we will never do anything more challenging in our lives than to serve these objectives," Kissinger said. "I would say all of us, except one."
Clinton, who served four years as President Barack Obama's top diplomat, is widely considered the frontrunner for the Democrat's presidential nomination in 2016. She has hinted at thinking about running for the job and has a cadre of groups organizing around the possibility that she runs.
Joining Kissinger and Clinton on stage for the groundbreaking were former secretaries James Baker, III, Madeleine Albright, and Colin Powell -- along with current Secretary of State John Kerry.
During her short remarks, Clinton heaped praise on her colleagues and told the audience that Kissinger has "written the book on diplomacy."
While Kissinger's joke was not an obvious joke about Clinton, the former top diplomat has been known to tease his successor about running for president.
Shortly after Clinton left the State Department in 2013, Kissinger gave a nod to Clinton 2016 while presenting an award to the former first lady.
"At least four secretaries of state became president," Kissinger joked during remarks at the annual Atlantic Council awards dinner in Washington. "And that sort of started focusing my mind even though there was a constitutional provision that prevented me from doing it. I thought up all kinds of schemes to get around that."
Then, adopting a more serious tone, he continued. "I want to tell Hillary that when she misses the office, when she looks at the histories of secretaries of state, there might be hope for a fulfilling life afterwards."
Clinton did not directly respond to Kissinger on Wednesday, but did do so in 2013.
"When I became secretary of state, I spent a lot of time thinking about my illustrious predecessors -- not primarily the ones who went on to become president," Clinton said to laughter.
Kissinger recently told NPR that although Clinton "would be a good President," he would still vote for the Republican nominee.
CNN's Mary Grace Lucas contributed to this report.