Doppelgänger stars Roy Thinnes, Ian Hendry, Lynn Loring, Loni von Friedl and Patrick Wymark.
Outside Europe, it was released as Journey to the Far Side of the Sun, the title by which it is now more commonly known.
Set in 2069, the film concerns a joint European-NASA mission to investigate a newly-discovered planet that lies parallel to Earth on the other side of the Sun. The mission ends in disaster when one of the astronauts (Hendry) is killed, after which his colleague (Thinnes) realises that the planet is a mirror image of Earth.
The first major live-action film to be produced by the Andersons, Doppelgänger was shot between July and October 1968 at Pinewood Studios and on location in England and Portugal.
The relationship between director Robert Parrish and Gerry Anderson became strained as filming progressed, while creative disagreements between Gerry and his business partner John Read, the film’s director of photography, led to Read leaving Century 21.
Although the Andersons wrote adult themes into the script in an attempt to distinguish Doppelgänger from their children’s productions, cuts were needed to allow the film to be certified A by the British Board of Film Censors.
Actors and props from the film were re-used during the production of the Andersons’ first live-action TV series, UFO.
Doppelgänger premiered in August 1969 in the United States and October 1969 in the United Kingdom.
The film’s final scene was filmed in Heatherden Hall at Pinewood Studios, where the Sylvia Anderson Estate is now based.
The film is available on DVD and Blu-ray.