Downing Street has confirmed that Boris travelled to the royal residence on Saturday before returning to London on Monday, but it is not known whether his wife Carrie and their 16-month old son Wilfred joined him.
"The PM was in Balmoral over the weekend. It was an entirely private visit," the Prime Minister’s official spokesman said.
WATCH: Inside Balmoral - The Royal Family's Idyllic Scottish Retreat
Boris and Carrie last visited the Queen’s Scottish retreat in 2019, before their son was born, and were reportedly forced to cancel their trip last year following the pandemic.
The Queen has had several visitors at her Scottish home this summer, including the Duke and Duchess of Cambridge and their children, Prince George, Princess Charlotte and Prince Louis, the Prince of Wales and the Duchess of Cornwall, and Princess Eugenie, Jack Brooksbank and their six-month-old son August.
Boris Johnson last visited the Queen at Balmoral in 2019
In the ITV documentary, Our Queen at Ninety, Princess Eugenie spoke out about the wonder of Balmoral. "It's the most beautiful place on earth," she said. "I think granny is the most happy there, I think she really, really loves the Highlands... Walks, picnics, dogs—a lot of dogs, there's always dogs! And people coming in and out all the time."
Her annual summer break supposedly includes barbeques, walking and horse riding among the whopping 50,000 acres.
However, the 95-year-old monarch interrupted her break on Sunday to share a personal note of congratulations following the end of the Paralympic Games in Tokyo.
The Queen's Scottish residence, Balmoral Castle
A message from was shared on the Royal Family's social media accounts. It read: "I offer my warm congratulations to Paralympic athletes from Great Britain and Northern Ireland, and indeed to the athletes of all Commonwealth countries, on their enormous success at the Tokyo Games.
"The commitment, dedication and adaptability shown by you, and your support teams, during the exceptional circumstances of the last 18 months has been inspirational. Your performances have lifted the nation and your triumphs been celebrated by us all.
"I send my very best wishes to all those who have contributed to the success of these memorable Games. ELIZABETH R."