President Trump visited London in 2018 under a cloud of protests. He visited the Queen at Buckingham Palace but broke convention by arriving late. The worst aspect was that he left the elderly lady standing for almost 15 minutes. Then he defied further protocols by walking in front of her.
Despite this, Trump claimed that he had a great working relationship with the Queen. He extended his sympathies after she passed and reminisced about her sense of humor. The polarizing President appeared sincere in his condolences (via Newsweek).