Sept. 16 (UPI) -- U.S. President Donald Trump was due to touchdown in Britain later Tuesday as he embarks on an unprecedented second state visit to the United States' closest ally as the guest of King Charles.

Trump and first lady Melania Trump will be met from Air Force One by Foreign Secretary Yvette Cooper, U.S. Ambassador to the U.K. Warren Stephens and Viscount Hood, King Charles' lord-in-waiting, before being whisked off to Windsor Castle, their main base for a packed schedule of events.

The visit gets underway in earnest Wednesday morning when the Trumps will be formally welcomed with a gun salute fired from the east lawn of Windsor Castle and the Tower of London, 25 miles away, simultaneously.

They will then ride a carriage through the estate in the company of the king, Queen Camilla, Prince William and Princess Catherine along a route lined with military personnel and music provided by the bands of the Royal Marines, army and Royal Air Force.

They will be greeted by a honor guard on arrival at the castle before lunch in the state dining room, followed by a tour of the royal art collection.