The Star Trek star was overjoyed when the famed director personally reached out to offer him the part of Archie Hicox in the 2009 film.
But Pegg was devastated when he realised his lead role in Steven Spielberg's The Adventures of Tintin: The Secret of the Unicorn was scheduled to shoot at the same time as Tarantino's project.
The actor had to choose between the two films and he eventually turned down the chance to star opposite Brad Pitt and Diane Kruger in Inglourious Basterds. The part eventually went to Michael Fassbender - and Pegg is still reeling over the tough decision.
He tells Britain's News of the World, "It was a horrible decision to make. I remember sitting on my own in a hotel room for an hour, having to decide which one to do. It was agony."