South Korea remains a deeply conservative society where extramarital affairs were a criminal offence until 2015, with some offenders — both the straying spouse and the lover — having been slapped with jail terms.
Affairs remain grounds for civil legal action.
The 74-year-old former German leader announced in January that he would marry Kim So-yeon, a South Korean translator 26 years his junior, after his fourth marriage fell apart.
Schröder's colourful private life and multiple marriages previously earned him the nickname “Audi man”, a reference to the German carmaker's four-ring symbol.
Kim and her husband divorced in November. Doris Schröder Kopf, the former leader's fourth wife, said last September in the process of divorcing him that Kim had played a part in the breakup.
The two started dating each other while both were still married, Kim's ex-husband claimed, suing Schröder for 100 million won ($94,000) in damages for “unbearable mental distress”, Yonhap news agency said.
The suit had been filed in the Seoul Family Court, it said, without disclosing the husband's name.
“The accused (Schröder) continued extramarital affairs with Kim knowing she is a married woman, causing unbearable mental distress,” it quoted the husband as saying in a document submitted to the court.
“Our marriage eventually fell apart, and the accused should be held responsible for his action,” it said.
Schröder insisted in January that Kim had nothing to do with the breakup of his marriage.
Kim is a Seoul representative of the Economic Development Agency of the German state of North Rhine-Westphalia and has worked as a Korean translator for Schröder.
The Social Democrat served as German chancellor from 1998 to 2005 and instituted labour market and welfare reforms which angered the left of his party.