Mr Reagan was in the city to deliver the Churchill Memorial Lecture at London's Guildhall as well as private meetings with the Queen and Prime Minister, Margaret Thatcher.
He and his wife Nancy were staying at Battersea Lodge, the home of American magazine publisher Malcolm Forbes.
Following the lecture, he was the guest of honour at a dinner hosted by Mrs Thatcher at 10 Downing Street.
The following day he attended a lunch with the Queen and the Duke of Edinburgh at Buckingham Palace.
And during a private ceremony, the former president became an Honorary Knight Grand Cross of the Most Honourable Order of the Bath, one of the highest orders of chivalry.
The Order of the Bath is the most senior knighthood that can be bestowed on a non-royal foreigner.
He was barred from adopting the title "Sir'' but he was able to wear the insignia and use the initials GCB after his name.
After the ceremony, Mr Reagan said: "I feel greatly honoured. I cannot say how proud I am to receive it.''
The Queen had met Mr Reagan, who served as the 40th President of the United States, from 1981 to 1989, a number of times during his two terms in office.
In his first trip to the United Kingdom since becoming President, he visited the monarch at Windsor Castle in 1982.
They took a horse ride together around the grounds of the castle and Reagan became the first President to stay overnight at the castle.
In 1983, The Queen and Prince Philip travelled to California to visit the Reagans at their ranch in Santa Barbara.
The royal couple arrived during a storm and had an interesting journey to his hilltop ranch.
According to a newspaper report from the time, the route involved "a narrow, twisting, steep obstacle course of flooded streams, washed-out sections, downed tree limbs and falling boulders".
However, Her Majesty’s Press Secretary was later quoted as saying: “She found the trip delightful and terribly exciting.”
Mr Reagan's wife Nancy later spoke about the Queen and Prince Philip's visit to their ranch in her memoirs.
"We had told them about the ranch during our visit to Windsor Castle, and the Queen was dying to go out riding with Ronnie,'' she writes. But there was heavy rain through the visit.
"The Queen had a wonderful attitude,'' she recalled. "'Don't be silly,' she said when I tried to apologise. `This is an adventure'.''
The queen and prince had a full schedule that week as they also visited San Francisco.
They were accompanied by Mrs Reagan down the steps of the plane on a rainy day at San Francisco International Airport. They were greeted by former San Francisco Mayor Dianne Feinstein and visited Davies Symphony Hall.
"This kind of weather happens in California every few centuries," joked Mayor Feinstein. She presented the Queen a bronze plaque and working key to Mission Dolores.
Actress and singer, Mary Martin, sang the popular Broadway and film tune Getting to Know You at the event and Tony Bennett sang his classic, I Left My Heart in San Francisco.
The royal couple had a private lunch at Stanford University, then toured Hewlett Packard before a private dinner at the de Young Museum in San Francisco.
The Queen and Prince Philip continued their west coast trip going north to Sacramento and Yosemite.
The Bay Area trip ended with a "Queen's Day" where spectators waved goodbye to the royal couple as they boarded the Britannia.
After receiving his knighthood in 1989, Mr Reagan flew to France on the next leg of his European journey where he was admitted as one of 12 foreign dignitaries who are associate members to the 200-year-old Institut de France during a trip to Paris.
In 1993, another former US President, George H.W. Bush, was awarded an honorary knighthood by the Queen as he and his wife Barbara attended a lunch at Buckingham Palace.
The award, recommended by Foreign Secretary Douglas Hurd, was said to mark the Government's close relationship with the Bush administration, particularly during the Gulf War in 1991.
In a tribute, after the former president died in December 2018, the Queen said: "President Bush was a great friend and ally of the United Kingdom. He was also a patriot, serving his country with honour and distinction in Office and during the Second World War."