(CNN) The State Department's top official for arms control will depart her post next month after months of controversy, triggered by the revelation that she had not disclosed a close relationship she once had with the former boyfriend of Russian agent Maria Butina.

Andrea Thompson is leaving as the Trump administration continues to seek a major nuclear deal with Russia and China after the collapse of the Intermediate Range Nuclear Forces Treaty. The multilateral deal has shown no signs of progress.

Secretary of State Mike Pompeo announced Thompson's departure in a statement on Friday.

"Under Secretary for Arms Control and International Security Andrea Thompson is a dedicated public servant who brought over 25 years of military experience to her role at the State Department," Pompeo wrote. "Her wealth of knowledge, experience, and leadership skills will be missed. I thank her for her commitment to the State Department's mission and for her decades of service to the United States of America. I wish her all the best in her future endeavors."

Thompson sent a letter to President Donald Trump a few weeks ago saying she would be leaving her job, but she is not officially departing until late October, according to a source who's close with her.

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