The wooden chest, which was being used as a TV stand and drinks cabinet, was a Japanese antique worth millions.
It was owned by an unnamed French engineer living in London who bought the 5ft long box for £100 in 1970 at a private sale without realising its value.
After his recent death the antique surfaced during a clearout of his house and was sold at auction.
The container, made of cedar wood and gold lacquer, was identified as a lost Japanese chest dating back to 1640.
London’s Victoria and Albert Museum had been searching worldwide for it since 1941, the last recording of it.
The chest – one of only 10 in the world – sat undetected at the owner’s house in South Kensington, less than a mile from the museum, until 1986 when he moved.
It has now been bought at auction by Amsterdam’s Rijksmuseum for £6.3 million pounds – £6.1 million higher than the estimate of £200,000.
Menno Fitski, the curator of East Asian art at the Rijksmuseum, said: “The thing to note about this chest is that it is the best of the best. It was the best when it was made and the same still applies today.
“It has an incredible back story which makes it all the more special. Amazingly it only surfaced when the owner died and his family were having a clear-out.
“The quality is the highest and the level of detail is incredible. There was a real feeling at the auction that this piece belonged at our museum.
“To be able to add such a significant item to our collection is a real honour.”
The intricate chest is decorated inside and out with gold lacquer depticting Japanese myths including the Tale of Genji.
It was made in 1640 in Kyoto by master crasftsman Kaomi Nagashige on commission for the Dutch East India Company.
In 1658 it was acquired by Cardinal Jules Mazarin, then the chief minister of France, for his extensive art collection and then passed down through his family.
British poet William Beckford bought it in 1802 and through his daughter Euphemia, wife of the Duke of Hamilton, it was included in the Hamilton Palace sale in 1882.
It was later acquired by prominent collectors Sir Trevor Lawrence and then Welsh colliery owner Sir Clifford Cory – but following Cory’s death in 1941 it disappeared off the radar.
Unknown to experts, it had been bought by a Polish doctor living in London who, unaware of its origins, sold it to a French engineer for just £100 in 1970.
When the Frenchman retired he moved from England to the Loire Valley in France, taking the chest with him.
The sum paid by the Rijksmuseum is thought to be the second highest ever paid at auction for Japanese art after a 12th century lacquered Buddha sold for £6.7 million in 2008.