President Donald Trump fired National Security Advisor John Bolton Tuesday, revealing his decision in a Tweet saying “his services are no longer needed at the White House.”

“I informed John Bolton last night that his services are no longer needed at the White House,” Trump tweeted. “I disagreed strongly with many of his suggestions, as did others in the Administration, and therefore I asked John for his resignation, which was given to me this morning. I thank John very much for his service. I will be naming a new National Security Advisor next week.”

Bolton, however, disputed Trump’s claims. On Twitter Bolton said he offered to resign Monday night but Trump responded that they would discuss the matter Tuesday.

According to recent reports the animus between Bolton and Trump was based on substantial disagreements on the handling of North Korea, Iran and Afghanistan. Bolton, who was formerly the United Nations Ambassador under President George W. Bush, disagreed with Trump on pursuing openly diplomatic channels with leaders in Iran and North Korea. Bolton did not trust the hard-line leaders.

Kim Jong-un, the North Korean dictator, was one major area of disagreement. Kim refused to surrender the nuclear arms program and continued short-range missile tests despite promises that these programs would be dismantled. According to the recent reports, Trump has also discussed meeting with Iranian President Hassan Rouhani if the circumstances permitted.

This is John Bolton’s resignation letter to President Trump: