The resignation of Ahn Hee-jung who came second to Moon Jae-in in the contest to select the Democratic Party's presidential candidate last year makes him the latest and most prominent figure in a swirling #MeToo movement in what is still a male-dominated society.
One of his secretaries told a television interviewer on Monday that he had raped her four times since hiring her in June.
Kim Ji-eun told JTBC that the last straw came when Ahn called her into his office on the night of February 25 and apologised for having hurt her, talking about the country's ongoing #MeToo movement.
"And then he raped me again," she said, sighing and holding back tears.
She also accused Ahn of sexually assaulting others and said she would file a criminal complaint against him Tuesday.
Following the TV interview, the ruling Democratic Party held an emergency meeting and expelled Ahn with immediate effect.
Hours later, Ahn, 52, announced his resignation as governor of South Chungcheong Province and retirement from public life.
In the Democratic Party's process to select its presidential candidate last year, Ahn was runner-up to Moon, who went on to win the election in May.
Ahn had been tipped as a front-runner among liberal presidential hopefuls to succeed Moon who can only serve one term with South Korean conservatives reeling from the massive corruption scandal that led to the ouster of former president Park Geun-hye.
Moon last month threw his support behind the #MeToo campaign spreading across the country, urging measures to combat the widespread abuse of women and punish offenders.
A growing number of South Korean women have accused prominent figures of sexual abuse, making headlines in a country that remains deeply conservative despite economic and technological advances.
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