Chisum, which is on ITV4 this weekend, was John Wayne’s first movie of the 1970s, which would also be the Western legend's final decade.

The film was based on the Lincoln County War of 1878 with Duke starring as John Simpson Chisum, a wealthy cattle baron of the American West.

The 62-year-old actor was playing a 54-year-old man, so had to go out of his way to hide his advancing age, having cosmetic surgery in September 1969 – a month before filming began.

As usual, Wayne wore his hairpiece and had make-up applied to appear more youthful than he was.

Meanwhile, Patric Knowles, who played Henry Tunstall, was labelled as the older man in the movie, even though at 58 he was four years younger than Duke.

As was the case in his later films, Wayne had a stunt double and ended up being left very disappointed by the end of the movie.

It turned out it was really obvious it wasn’t him as Chisum in the final fight scene between his character and Forrest Tucker’s Lawrence Murphy.

Despite this disappointment, after the film’s Dallas premiere, Duke went out of his way to show incredible kindness to sick child fans.

According to the John Wayne estate: “Did you know? One writer tells of the night he and Duke were in Dallas for the premiere of Chisum.

“Returning late to his hotel, Duke found a message from a woman who said her little girl lay critically ill in a local hospital. The woman wrote, ‘It would mean so much to her if you could pay her just a brief visit.’

“At 3 o'clock in the morning he took off for the hospital where he visited the astonished child and every other patient on the hospital floor who happened to be awake.”