The King has written to Donald Trump after the former US President survived an assassination attempt.
Charles's message was delivered on Sunday via the UK Embassy in Washington DC.
Buckingham Palace said the contents of the correspondence will be kept private, but it is understood that the King's message was in keeping with Prime Minister Sir Keir Starmer's conversation with Mr Trump, in which he condemned the violence, expressed his condolences for the victims and their families, and wished the former president and those injured a quick recovery.
Mr Trump, who served as the 45th President of the United States from 2017 to 2021, suffered a gunshot wound to the ear during the assassination attempt at a campaign rally in Butler, Pennsylvania on Saturday.
After being treated at a local medial facility where his injuries were not found to be serious, he returned to his home in New Jersey.
Mr Trump later posted a statement on Truth Social, saying he was shot by a "bullet that pierced the upper part of my right ear".
He added: "I knew immediately that something was wrong in that I heard a whizzing sound, shots, and immediately felt the bullet ripping through the skin. Much bleeding took place, so I realised then what was happening. GOD BLESS AMERICA!"
Three audience members were also struck by bullets, including one which killed 50-year-old Corey Comperatore, who died shielding his daughters.
The FBI later named Thomas Matthew Crooks, 20, as the shooter, who fired shots into the rally from the roof of a nearby building outside the venue. He was subsequently killed by a Secret Service Counter Assault Team sniper.
Family reactions and President's statement
Former First Lady and Mr Trump's wife, Melania Trump, wrote in a statement: "When I watched that violent bullet strike my husband, Donald, I realized my life, and Barron's life, were on the brink of devastating change. I am grateful to the brave secret service agents and law enforcement officials who risked their own lives to protect my husband.
"To the families of the innocent victims who are now suffering from this heinous act, I humbly offer my sincerest sympathy. Your need to summon your inner strength for such a terrible reason saddens me."
Donald shares son Barron, 18, with Melania. He shares Donald Jr, Ivanka and Eric with his first wife, the late Ivana Trump. Daughter Tiffany was born from his second marriage to Marla Maples.
In response to the assassination attempt on Mr Trump, US President Joe Biden said: "I'm grateful to hear that he's safe and doing well. I'm praying for him and his family and for all those who were at the rally, as we await further information.
"Jill and I are grateful to the Secret Service for getting him to safety. There's no place for this kind of violence in America. We must unite as one nation to condemn it."