Diana left personal items to her brother, Earl Spencer, to be "looked after" until her sons turned 30. Her youngest, Harry, will be 30 next year.
The museum's collection includes 28 dresses, two tiaras, priceless family jewelry, along with pictures, letters and home movies.
“It will close worldwide in August 2014,” a spokesman for Diana's brother told the Telegraph.
Diana's family members opened the museum at their Althorp estate in 1998, a year after she died in a Paris car crash.
There's speculation that Diana's possessions will next be on display at Kensington Palace, where she once lived and where the Duke and Duchess of Cambridge will soon set up residence.
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