Jimi Hendrix's Epiphone acoustic guitar realised £209,000 ($260,414) at Bonhams London last week.
It proved the highlight of an auction of entertainment memorabilia, selling for almost double its £120,000 ($149,605) estimate.
Hendrix bought the guitar in New York in 1967, while touring with the Jimi Hendrix Experience.
He brought it back with him to London, where he regularly used it to write music. His then partner, Kathy Etchingham, explains: "We shared the flat in Upper Berkeley Street with Chas [Chandler - Hendrix's manager] and Lotta [Chandler's partner], but had our own bathroom.
"Ours was fully tiled and had no window but a beautiful echo, a good sound that Jimi liked so he would sit on the loo and play!"
Hendrix had been forced to stop using an electric guitar and an amplifier at home after being booted out of his previous flat following noise complaints.
Etchingham said: "When working on a song 'Jimi would pick up and then play the acoustic, then pick up a Strat and play that unplugged, listening to it without an amp.
"He constantly played it to work out riffs and song arrangements including his own version of Dylan's 'All Along The Watchtower'."
The guitar last sold for £62,000 ($77,136) at a 2001 sale, resulting in growth of 8.4% per annum in the intervening years.