£6.5 million which was invested and gathered substantial interest, and an estimated £10 million was given to each son upon turning 30 years old in 2012 and 2014 respectively. Many of Diana's possessions were initially left in the care of her brother who put them on show in Althorp twice a year until they were returned to the princes. They were also put on display in American museums and raised two million dollars for charities. Among the objects were her dresses and suits along with numerous family paintings, jewels and two diamond tiaras. Diana's engagement ring and her yellow gold watch were given to Harry and William, respectively. The brothers eventually exchanged mementos and William later passed the ring to his wife, Catherine Middleton. The ownership of Diana's wedding dress was also given to her sons. In addition to her will, Diana had also written a letter of wishes in which she had asked for three-quarters of her personal property to be given to her sons, and dividing the remaining quarter (aside from the jewellery) between her 17 godchildren. Despite Diana's wishes, the executors (her mother and sister) "petitioned the probate court for a "variance" of the will", and the letter of wishes was ignored "because it did not contain certain language required by British law". Eventually, one item from Diana's estate was given to each of her godchildren, while they would have received £100,000 each, had a quarter of her estate been divided between them. The variance also prevented the estate from being distributed between her sons at the age of 25 but postponed it until they were 30. Diana also left her butler Paul Burrell around £50,000 in cash. Subject of U.S. government surveillance In 1999, after the submission of a Freedom of Information request by the Internet news service apbonline.com, it was revealed that Diana had been placed under surveillance by the National Security Agency until her death, and the organisation kept a top secret file on her containing more than 1,000 pages. The contents of Diana's NSA file cannot be disclosed because of national security concerns. The NSA officials insisted Diana was not a "target of [their] massive, worldwide electronic eavesdropping infrastructure." Despite multiple inquiries for the files to be declassified—with one of the notable ones being filed by Mohamed Al-Fayed—the NSA has refused to release the documents. In 2008, Ken Wharfe, a former bodyguard of