Richard Dowling was jailed for five years and Annette Breakspear for eight. They were both 38 when the sexual abuse began, the MailOnline reported.
The fashion retail manager said that the abuse started when he was playing a board game when his stepmother, now also 62, who ended up being "completely naked."
In another event he was forced to give his stepmother, who was handcuffed naked on the bed, a "goodnight kiss" before his father joined them.
He told The Sunday Mirror: "She'd instruct me on what to do. Sometimes when Dad wasn't there she'd ask me into her room for fondling and intercourse."
The stepmother's abuse started happening even when his father, who used to work for the Ministry of Defence, wasn't at home.
In one incident his father told his son to perform a sex act on his stepmother and punched him when he refused.
It only came to an end after Richard Dowling's relationship with Annette Breakspear broke down in 1996 and they moved to Weymouth, Dorset.
At this time Daniel Dowling, then 16, was being abused by another paedophile.
Police found naked pictures of him at the paedophile's home and the teenager revealed his childhood trauma to a psychologist, but no arrests were made after his father and stepmother were interviewed.
It was also claimed in court that police treated the teenager "shoddily" in interviews.
Almost two decades after the abuse, Daniel Dowling had to take action to get justice for himself in 2015.
He secretly recorded a phone call with his father when the older man admitted to the abuse.
In court the father blamed his actions on "undiagnosed depression" and said that he was influenced by his partner who had a "Jekyll and Hyde character."
He admitted one count of cruelty to a child and two counts relating to sexual offences involving a child. He was found not guilty of one count of indecent assault.
The judge at the trial said: "The damage is incalculable. The abuse of trust is monstrous."
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