north korea is shaking up its military leadership. the country's top three officials are out. their replacements younger staunch kim loyalists who also is saido have experience interacting with foreign delegations. now this comes as preparations are in full swing for the june 12th summit. the first time a sitting u.s. president will meet with a north korean leader. and cnn international diplomatic editor nic robertson is in seoul, south korea. he joins us now live. good to see you, nic. let's start with the replacement of the top threeary officials by kim jong-un ahead of the june summit. what might this signal, do you think? >> so it's the defense chief. it's the head of the army and the head of the army's political bureau. these obviously very influential positions. the head of the political bureau for the korean people's army is