Jeong Ho-seong, former personal secretary to former President Park Geun-hye, watches Park's press conference at BEXCO, Busan, Dec. 12, 2014. Joint Press Corps

President Yoon Suk Yeol has taken flak from the opposition for appointing a former presidential secretary who used to work for impeached former President Park Geun-hye as a new secretary for civil and social agenda.

According to the presidential office, Friday, Jeong Ho-seong, who served a prison term for his involvement in the massive corruption scandal involving Park, began working as the third secretary for civil and social agenda.

Jeong is a long-time aide for former President Park, serving for her since 1998 when Park became a lawmaker. After Park took office in 2013, Jeong was appointed as a presidential personal secretary to manage the president's schedule and write some of her public addresses.

Back then, Jeong was mentioned as one of "the doorknob trio," a term that refers to three key presidential secretaries of Park who exerted significant influence over all state affairs.

During Park's impeachment process, Jeong was sentenced to an 18-month prison term for leaking confidential documents including the president's speeches to Choi Soon-sil, Park's long-time civilian confidant, upon Park's orders. The prosecutor who indicted Jeong at the time was Yoon Suk Yeol, who was one of the lead prosecutors of the special counsel probe on Park and who later went on to become the nation's president.

"Yoon is building a fortress to hide himself," DPK spokesperson No Jong-myeon said. "This time, he hired former presidential secretary Jeong, who was one of the doorknob trio. Jeong is the main culprit of former President Park's scandal due to his leaking documents to Choi, and he was detained and indicted by Yoon himself.

Minor opposition Rebuilding Korea Party Chairman Cho Kuk also slammed Yoon's decision.

"Isn't he one of the people who ruined the Park Geun-hye administration?" Cho said during a radio interview with broadcaster MBC. "During that investigation and prosecution of Jeong, Yoon pounded a lot of criticisms and accusations. There must be a reason why he was hired. He must have some special skills or connections, but I think it's shameful."

In the Yoon administration, there are three secretaries under the senior presidential secretary for civil and social agenda — the secretary for social integration, the secretary for civil society and communication and the secretary for civil affairs.

The presidential office will soon rename the position as the first, second and third secretary for civil and social agenda, with Jeong being appointed as the third secretary to take care of communications with religious and civic groups.