The collection of letters, mementoes and photographs showing the couple at Balmoral and Osborne, the queen's home on the Isle of Wight, were stored in a trunk belonging to one of Brown's descendants in Royal Deeside.
The collection has never been made public before. It was discovered by Douglas Rae, an executive film producer, and Jeremy Brocks, a writer, when they began their research into the film Mrs Brown, starring Judi Dench, which was shown on television last night.
Mr Rae said the letters gave a useful insight into the Queen's relationship. "There is no doubt in my mind they were written by two people who shared an intimate friendship," he said. "We even found a Valentine card from the Queen which read `to my best friend JB from his best friend VR'."
Mr Rae, who has not named the family who own the letters, said their contents and whereabouts would remain secret.Reuse content