The artwork will return to the capital 100 years to the day since it was last seen in the UK, it’s been announced.
So, who is its painter Thomas Gainsborough, who is the person in the Blue Boy painting, and why is it so famous?
When was The Blue Boy painted - and who is the boy?
The Blue Boy was painted as an oil canvas in approximately 1770.
The Blue Boy, which is regarded as Gainsborough's most famous work, is thought to be a portrait of Jonathan Buttle, the son of a wealthy hardware merchant - although this has never been confirmed.
Gainsborough believed in using the surrounding backdrop to set the scene for his subjects’ mood and character.
He more commonly painted landscapes and once admitted that he only painted portraits for the income they brought him, as landscapes were his real love.
When was the painting first unveiled?
The portrait was unveiled in 1770 at the Royal Academy of Arts in London and, as Gainsborough had hoped, it enjoyed a very positive reception at this prestigious venue which had just opened.
People liked the use of the vibrant blue colour and thoughtful brush strokes, which made it an instant success.
Who owns the painting and where is it now?
Initially, the subject of the portrait, Jonathan Buttall, owned the painting. However, in 1796, he was declared bankrupt and sold it to John Nesbitt, a politician at the time.
At the turn of the 19th century, the portrait was owned by well-known portrait artist John Hoppner but in 1809 it was sold to Earl Grosvenor.
It remained in his family for over 100 years until it was sold by the second Duke of Westminster.
While the original painting was exhibited at the British Institution and the Royal Academy, it was also reproduced as prints, which were available to the general public.
By 1920, it had earned its place as one of the iconic paintings of English heritage.
In 1921, however, The Blue Boy was sold to dealer Joseph Duveen who had bought it for railroad tycoon Henry Edwards Huntington who lived in America.
This caused an outcry among many people in England at the time, who believed that the painting should stay in its homeland.
Ahead of The Blue Boy's departure for its new American home, it was exhibited for a final time by The National Gallery, attracting an incredible 90,000 people.
Charles Holmes, director of the gallery, is said to have inscribed "Au Revoir, C.H." on the back of it.
It is currently in the Huntington Library, Art Museum, and Botanical Gardens in California.
When will the painting return to the UK and where will it be shown?
The Blue Boy will be on show from January 25 until May 15, 2022 in London’s National Gallery, in Trafalgar Square, not far from where it was exhibited 100 years ago.
It will then return to America permanently.
Dr Gabriele Finaldi, director of the National Gallery, said: “The loan of Gainsborough's Blue Boy to the National Gallery is truly exceptional and a unique opportunity for visitors to see Gainsborough at his dazzling best.
“Rich in historical resonances, a painting of supreme poise and elegance, The Blue Boy is without doubt a masterpiece of British art.”