President Trump announced via Twitter his pick to replace ousted National Security Adviser John Bolton: the U.S.’s current chief hostage negotiator Robert O’Brien.

I am pleased to announce that I will name Robert C. O’Brien, currently serving as the very successful Special Presidential Envoy for Hostage Affairs at the State Department, as our new National Security Advisor. I have worked long & hard with Robert. He will do a great job! — Donald J. Trump (@realDonaldTrump) September 18, 2019

O’Brien currently works closely with the families of American hostages and advises the government on how to properly handle the return of Americans held hostage overseas.

Most recently, O’Brien was involved with trying to get American rapper A$AP Rocky released from custody in Sweden. O’Brien attended one of Rocky’s hearings in Sweden, according to the New York Times. Rocky was not being held as a hostage, but rather was arrested for allegedly being involved in an assault. He was eventually released and returned to the U.S.

O’Brien has previously worked under former Secretaries of State Condoleezza Rice and Hillary Clinton as the co-chairman of the State Department’s Public-Private Partnership for Justice Reform in Afghanistan, according to the State Department.

O’Brien also worked with Bolton during the George W. Bush administration as a representative to the 60th session of the United Nations General Assembly. O’Brien was also a Major in the U.S. Army Reserve.

Just hours before the announcement, Trump included O’Brien on a list possible candidates to replace Bolton. He shared the narrowed list with reporters on Air Force One Tuesday evening. Most of the candidates are not as well-known as people who Trump tends to gravitate toward for administration posts.

The list included:

● U.S. hostage negotiator Robert O’Brien

● Assistant to the Chairman of the Joint Chiefs of Staff Army Maj. Gen. Ricky Waddell, who has also been the deputy national security adviser

● Energy Department Undersecretary for Nuclear Security Lisa E. Gordon-Hagerty

● Ex-Bolton chief of staff Fred Fleitz

● National Security Adviser to Vice President Pence retired Army Lt. Gen. Keith Kellogg

While speaking to reporters on Tuesday, Trump praised O’Brien in particular, calling the hostage negotiator “fantastic.” He also had some kind words for Kellogg and his loyalty: “He’s been with me from the beginning.”

White House press secretary Stephanie Grisham later clarified to reporters that there were also other names being considered to replace Bolton.

“As the President said when speaking to the pool, the names of candidates mentioned for the NSA position was not the full list, and there are others being considered,” she said.

Bolton was ousted last week via presidential tweet after butting heads with enough key members of Trump’s administration that the President deemed it was time for his exit.

It’s been reported that Trump and Bolton were recently at odds over a since-canceled meeting with the Taliban at Camp David. Trump has, reportedly, often diverged from Bolton’s famously warmongering perspective on foreign policy. He also blamed Bolton for a failed U.S.-backed effort to force Venezuelan President Nicolás Maduro from office.