Scott Pruitt, who has been the focus of multiple ethics investigations during his nearly 17-month tenure as head of the Environmental Protection Agency, resigned Thursday.

In his resignation letter, obtained by the PBS NewsHour, Pruitt wrote that it was an “honor to serve” in Trump’s Cabinet, especially because of the “transformative work that is occurring.” But he added that “the unrelenting attacks on me personally, my family, are unprecedented and have taken a sizable toll on all of us.”

READ MORE: Scott Pruitt resigns as head of EPA, Trump says

President Donald Trump first announced the news on Twitter, saying he accepted Pruitt’s resignation. “Within the Agency Scott has done an outstanding job, and I will always be thankful to him for this,” he added. The president did not mention any of the more than 12 investigations into Pruitt’s potential ethics violations.

Andrew Wheeler, Pruitt’s deputy, is expected to take over as acting administrator of the agency on Monday.

Read Pruitt’s full resignation letter below.

Mr. President, it has been an honor to serve you in the Cabinet as Administrator of the EPA. Truly, your confidence in me has blessed me personally and enabled me to advance your agenda beyond what anyone anticipated at the beginning of your Administration. Your courage, steadfastness and resolute commitment to get results for the American people, both with regard to improved environmental outcomes as well as historical regulatory reform, is in fact occurring at an unprecedented pace and I thank you for the opportunity to serve you and the American people in helping achieve those ends.

That is why it is hard for me to advise you I am stepping down as Administrator of the EPA effective as of July 6. It is extremely difficult for me to cease serving you in this role first because I count it a blessing to be serving you in any capacity, but also, because of the transformative work that is occurring. However, the unrelenting attacks on me personally, my family, are unprecedented and have taken a sizable toll on all of us.

My desire in service to you has always been to bless you as you make important decisions for the American people. I believe you are serving as President today because of God’s providence. I believe that same providence brought me into your service. I pray as I have served you that I have blessed you and enabled you to effectively lead the American people. Thank you again Mr. President for the honor of serving you and I wish you Godspeed in all that you put your hand to.

Your Faithful Friend,

Scott Pruitt

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