John Bolton

Updated at 2:31 p.m. ET

President Trump has named Robert C. O'Brien, who has been his special envoy for hostage affairs, to be his new national security adviser.

Trump made the announcement in a Wednesday morning tweet.

"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!" Trump said.

Updated at 4:57 p.m. ET

President Trump has fired national security adviser John Bolton, the lifelong proponent of American hard power, after months of division between the men over the direction of foreign and national security policy.

Trump announced the news Tuesday on Twitter.