The title is something of a misnomer. Errol Flynn never really had a "secret life" but lived most of it out in public.
Born in Tasmania, he had a turbulent life doing various jobs until he made his theatrical debut at the Theatre Royal, Northampton. He was never much of an actor, but developed a reputation for exhibitionism by posing nude in front of a mirror for the benefit of workers in a local shoe factory.
He moved to Hollywood where he was fortunate enough to secure a long-term contract for Warner Brothers. After making his debut in programmers, he really established his reputation with swashbucklers such as CAPTAIN BLOOD (1935) and ROBIN HOOD (1939).
Offscreen he cultivated the image of a hard-drinking Lothario, sharing a house with David Niven that was dubbed "Cirrhosis by the Sea." He enjoyed a colorful sex life, even though he consciously boasted about the size of his equipment, so to speak.
In 1942 he was taken to court on charges of molesting underage girls. Although exonerated due to the machinations of a Hollywood lawyer, he was most likely guilty. Thereafter he appeared to be consciously destroying himself with a combination of drink, drugs and sex. He was finally cast off from Warner Brothers in the early Fifties, and thereafter led an itinerant life until he made perhaps two of the best films of his career including THE SUN ALSO RISES (1957), where he played a washed-up alcoholic.
All of his life was lived in the public eye; thus it seemed somehow appropriate that he should die of a heart attack in 1959, accused once more of molesting an underage girl Beverly Aadland.
This documentary told the truth about Flynn, but in truth seemed more preoccupied with revealing salacious details rather than telling us more about his character off screen (if he had such a character, that is).