WASHINGTON (AP) — The head of the Food and Drug Administration’s drug center abruptly resigned Sunday after federal officials began reviewing “serious concerns about his personal conduct,” according to a government spokesperson.

Dr. George Tidmarsh, who was named to the FDA post in July, was placed on leave Friday after officials in the Department of Health and Human Services’ Office of General Counsel were notified of the issues, HHS press secretary Emily Hilliard said in an email. Tidmarsh then resigned Sunday morning.

The departure came the same day that a drugmaker connected to one of Tidmarsh’s former business associates filed a lawsuit alleging that he made “false and defamatory statements,” during his time at the FDA.

The lawsuit, brought by Aurinia Pharmaceuticals, alleges that Tidmarsh used his FDA position to pursue a “longstanding personal vendetta” against the chair of the company’s board of directors, Kevin Tang.

Tang previously served as a board member of several drugmakers where Tidmarsh was an executive, including La Jolla Pharmaceutical, and was involved in his ouster from those leadership positions, according to the lawsuit.