The King has written privately to former President Trump after he survived an assassination attempt, Buckingham Palace has confirmed.
The message was delivered on Sunday via the UK embassy in Washington DC.
The contents of the letter have not been made public, but the BBC understands the sentiments are in keeping with those communicated by the prime minister over the weekend.
Mr Trump survived a shooting while he was speaking at a rally in Philadelphia on Saturday.
Prime Minister Sir Keir Starmer said he was “appalled” by the attack. In a call with the former US president on Sunday afternoon, Sir Keir is understood to have expressed his condolences for the victims and their families, and wished Mr Trump and those injured a quick recovery.
The former president was shot in the ear when a gunman opened fire at the Philadelphia rally.
One spectator was killed and two others were seriously injured. The suspected shooter, Thomas Matthew Crooks, was shot dead at the scene
Mr Trump, who raised his fist to the crowd while bleeding after the shooting, told the New York Post he was “supposed to be dead” and described the assassination attempt as a “surreal experience”.
He is due to speak this week at the Republican National Convention in Milwaukee, Wisconsin, where he is set to be formally confirmed as the party’s candidate for November’s presidential election.
Mr Trump says he has rewritten his speech in the wake of the shooting, and will use it to “bring the country together”.
UK politicians continued to condemn the attack on Monday.
Culture Secretary Lisa Nandy told BBC Breakfast she was “horrified and angry” at the assassination attempt and added it was “heartening” to see so many world leaders join the condemnation.
Shadow foreign secretary Andrew Mitchell told Sky News the shooting was “an appalling act of violence and wickedness” that has been “rightly condemned by everyone for what it is”.
In 2019 as Prince of Wales, Charles hosted then-President Trump and his wife Melania for afternoon tea at Clarence House during a Nato summit in London.
The late Queen Elizabeth hosted a state banquet for Mr Trump during a state visit to the UK earlier the same year.
