The Führer was reportedly heartbroken when Geli Raubal fell victim to a bullet from his own Walther pistol.
Officially it was suicide. But some historians believe he murdered her to keep their affair quiet.
The unsigned artwork showing Geli's resting place in the Central Cemetery in Vienna went up for sale today.
Ben Jones of auctioneers Mullock's said: "It's controversial but it is history at the end of the day."
Geli was the daughter of Hitler's half-sister Angela Raubal and 19 years younger than him.
Hitler (left) relaxing with Geli in 1930
The relationship began in 1925 when Angela became housekeeper at his mountain retreat and brought her two girls.
Geli was a spirited, flirtatious 17-year-old who called him "Uncle Alf". It is not clear whether the relationship was sexual.
But in September 1931 they were heard having a row. The next day, Geli, then 23, was found lying face down with a single bullet lodged in her lung.
Hitler was devastated and several times visited the grave depicted in the picture. It failed to attract a buyer at today's sale in Ludlow, Shrops.
Geli was killed by a single bullet
Four other paintings – all signed "A Hitler" and valued between £5,000 and £7,000 – also went unsold.
Auctioneer Mr Jones said it was the second time they had tried to sell the five pictures. He added: "They didn't go five years ago and have been in our office ever since."
But four other paintings attributed to Hitler were snapped up for £7,500.
Mr Jones said: "I've been asked, 'Who collects this?' But people can do what they want behind closed doors."
Most of Hitler's paintings were done before the First World War when he was destitute in Vienna. By the time Geli died he was 15 months away from becoming Chancellor.