The White House’s chief attorney, Don McGahn, will leave sometime this fall, President Trump tweeted Wednesday.

White House Counsel Don McGahn will be leaving his position in the fall, shortly after the confirmation (hopefully) of Judge Brett Kavanaugh to the United States Supreme Court. I have worked with Don for a long time and truly appreciate his service! — Donald J. Trump (@realDonaldTrump) August 29, 2018

McGahn had been the chief lawyer for the Trump campaign and helped oversee the successful confirmation of Neil Gorsuch to the Supreme Court and a raft of appointees to lower courts. But, like so many other Trump administration officials, his tenure ended up being increasingly defined by the Russia investigation.

McGahn both worked on the investigation in his role as White House counsel and was interviewed by Robert Mueller’s investigators several times as a witness to Trump’s possibly legally problematic behavior in responding to the investigation, especially the firing of James Comey. The New York Times reported that McGahn and his own attorney had been especially cooperative with Mueller’s team because he had feared that Trump was going to pin any obstruction of the investigation on him.

At least one of Trump’s allies seems caught by surprise about the announcement—and either didn’t believe or didn’t get briefed on the president’s tweet.

@realDonaldTrump I hope it’s not true McGahn is leaving WhiteHouse Counsel. U can’t let that happen — ChuckGrassley (@ChuckGrassley) August 29, 2018

While Trump has not announced McGahn’s successor, Axios reported Monday morning that it would most likely be Emmet Flood, a White House lawyer who is working on the Russia investigation.

Update, Aug. 29, 1:28 p.m.: Another senior Republican was seemingly stunned by the news—and remained almost incredulous. Senate Majority Leader Mitch McConnell said in a statement, “If the reporting is true about Don McGahn’s time at the White House coming to an end later this year, it will be sad news for our country,” implying there was a possibility the president’s statement about the employment of his own staffer might not be accurate.

Grassley and McConnell weren’t the only ones caught off guard by Trump’s tweet: McGahn himself did not know the tweet was coming, the Washington Post reported, and “he had not discussed his plans directly with Trump.”