Zephyr Teachout, Gov. Cuomo’s little-known Democratic-primary opponent, broke down in tears on the witness stand Thursday as she battled to stay on the ballot.

The Fordham Law professor started crying in Brooklyn Supreme Court when her own lawyer asked about the city apartment she shared in 2010 with a woman who died of cancer.

The proceedings were halted so she could compose herself after recalling former roommate Lynn Marie Ruse. “I still miss her,” Teachout explained.

The Cuomo campaign has challenged Teachout’s candidacy, claiming she hasn’t lived in the state for the past five years as required by election law.

Teachout insisted she’s been a New Yorker at least since 2009.

But it was only last month that she amended her 2009 and 2010 state tax returns to show she was a full-time resident, though she earlier reported spending no days in the state in 2009.

Teachout maintained that was a simple error caused by her self-filing using TurboTax.