Independent Vermont Sen. Bernie Sanders lost his cool Wednesday night when former New York City Mayor Michael Bloomberg called him the “best known socialist” who “happens to be a millionaire with three houses.”

A fiery end to what had already been a contentious Democratic primary debate, which included the billionaire businessman for the first time, was sparked by NBC anchor Lester Holt’s question to Sanders about two-thirds of voters being “uncomfortable with a socialist candidate for president.”

After seeming to question the poll’s results by pointing out his frontrunner status for the Democratic nomination, Sanders called Bloomberg’s earlier use of the word “communism” a “cheap shot,” contending his policies were more akin to “what goes on in countries like Denmark.”

When Sanders criticized “tax breaks and subsidies” for the rich, Bloomberg interjected: “What a wonderful country we have. The best known socialist in the country happens to be a millionaire with three houses. What did I miss here?”

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“Well, you missed that I work in Washington, house one,” Sanders responded defensively.

“That’s the first problem,” Bloomberg said.

“Live in Burlington [Vermont], house two,” Sanders said. “And like thousands of other Vermonters, I do have a summer camp. Forgive me for that. Where is your home? Which tax haven …” (RELATED: Topless Protesters Storm The Stage At Bernie Sanders Rally)

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“New York City, thank you very much,” Bloomberg responded. “And I pay all my taxes. And I’m happy to do it because I get something for it.”