Former U.S. Ambassador to the UN John Bolton will replace Lt. Gen. H.R. McMaster as White House National Security Advisor (NSA) on April 9, President Donald Trump announced in a tweet on Thursday.

The reshuffle follows the surprise announcement earlier in the month that Trump had accepted an invitation to meet North Korean leader Kim Jong Un “by May.”

It is also the second sacking of a senior administration official since the announcement, following the dismissal of Secretary of State Rex Tillerson on March 13.

“I am pleased to announce that, effective 4/9/18, @AmbJohnBolton will be my new National Security Advisor,”