New York City's deputy mayor for health and human services will leave her post at the end of September to accept a position with the city Health and Hospitals Corporation, Mayor Bill de Blasio's office said Monday.

Lilliam Barrios-Paoli -- the highest-ranking official to leave the administration since de Blasio took office in January 2014 -- will serve as chair of the HHC's board.

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"Her experience in government and devotion to social services are unparalleled, and she will be dearly missed at City Hall," de Blasio said in a statement. "Lilliam is an extraordinary public servant."

Barrios-Paoli thanked the administration and her team, saying she is "excited for this new phase."

Before de Blasio appointed her to his inner circle, Barrios-Paoli managed five city agencies under three mayors.