An adventurous gambler Nick Newlife from Oxford, believing that Federer will win his 7th Wimbledon singles title before 2019, placed the bet in 2003, reported Daily Mail.
Newlife placed a bet of 1,520 pounds at odds of 66 to 1 with bookmakers William Hill on Federer winning seven or more Wimbledon titles.
Seven years before the cut off, the bet has set the cash registers ringing at Oxfam.
Newlife passed away in 2009.
The 69-year old bachelor with no family and friends left the betting slip, along with all of his possessions, to Oxfam.
He was a landlord who lived alone in a three bedroomed semi-detached house set in a picture postcard countryside village.
Reacting to the news, Oxfam has said that legacies have a major contribution to their income.
"Legacies amount to 10 per cent of our total income from individuals, so they're essential to us, and as this case proves they can come in all shapes and sizes," Oxfam spokesman Stuart Fowkes said.
Federer beat Britain's Andy Murray 4-6, 7-5, 6-3, 6-4 yesterday to join Pete Sampras and William Renshaw as a seven-time Wimbledon champion and rack up his 17th Grand Slam win.