U.S. Secretary of Housing and Urban Development Julian Castro neither confirmed nor did a good job denying that he will become Hillary Clinton's running mate during his Monday night appearance on "The Late Show With Stephen Colbert."

Late last year, Clinton admitted that she was considering Castro as her vice presidential running mate in the 2016 race. However, the 41-year-old Mexican American official refused to share any new details on whether he is currently in training for the spot on the ticket.

"You sound a little bit like you're running for something," teased late night show host Stephen Colbert, after Castro talked about the work his department is doing to help homeless veterans.

"It's hard to get it out of your system," Castro jokingly snapped back.

At another point in the interview, Colbert directly mentioned speculation that Castro will join the Democratic front-runner on the campaign trail.

"There are rumors you're in vice president training camp," Colbert suggested. "What does that entail other than staying awake during the State of the Union?"

However, the former San Antonio mayor dismissed the question as being just a flattering suggestion.

Colbert ended the interview by asking Castro to brush up on his Spanish with flash cards. After several simple vocab words, the last card read, "Yo soy el vice presidente."

Castro saw the trick and pretended to get the phrase wrong, saying Colbert was the vice president.

Back in October, Castro endorsed the former secretary of state.

"I wanted to make sure to lend my support to the person that I believe would make the next president -- next," Castro said.

He also joined her at a campaign event to kick off "Latinos for Hillary" in Texas, declaring that Clinton "has a strong vision for America's future" and is the candidate best prepared to fix the broken immigration system.

Watch Castro's interview with Colbert below: