Sen. Mark Kirk Mark Steven KirkLiberal veterans group urges Biden to name Duckworth VP On the Trail: Senate GOP hopefuls tie themselves to Trump Biden campaign releases video to explain 'what really happened in Ukraine' MORE (R-Ill.), a freshman senator facing a tough reelection race in 2016, was caught on a microphone Thursday referring to bachelor Sen. Lindsey Graham Lindsey Olin GrahamMcConnell locks down key GOP votes in Supreme Court fight Will Republicans' rank hypocrisy hinder their rush to replace Ginsburg? Momentum growing among Republicans for Supreme Court vote before Election Day MORE (R-S.C.), who is running for president, as a “bro with no ho.”

Kirk can be heard in the clip below talking about Graham’s joke this week that he’ll have a rotating cast of first ladies if he wins the White House, because he is not married (starts at the 26-second mark).

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Kirk’s comments, made during a Senate Appropriations Committee markup, were not heard by reporters in the hearing room, but were audible on a livestream and highlighted by The Huffington Post.

“Did you see that? He’s going to have a rotating first lady. He’s a bro with no ho,” Kirk said, using a popular phrase that includes the disparaging term for women.

Kirk's spokeswoman, Danielle Varallo, told The Hill the senator was "joking with his colleague and immediately apologized to anyone offended by his remark."

Kirk, one of the most vulnerable Senate incumbents in 2016, is no stranger to controversial remarks. He drew criticism back in February for telling National Journal that the bodies of dead Americans should be “laid at the feet of the Democratic caucus” if there is a successful terrorist attack following a battle over Department of Homeland Security funding.

The first-term senator will likely face off against Rep. Tammy Duckworth (D-Ill.) in the general election next year.

Graham, a Republican from South Carolina, is seeking to become the first bachelor president since Grover Cleveland, who later married in office in 1886, one year after the beginning of his first term.

This story was updated at 4:14 p.m.