Forty years ago, on Nov. 18, 1978, more than 900 members of cult group People’s Temple were led by their leader, Jim Jones, to commit mass suicide by cyanide in the Jonestown settlement of Guyana — and his two surviving sons are still healing from the tragedy.

Stephan Jones and his adopted brother, Jim Jones Jr., who were both 18 then, have come forward for a four-part docuseries on SundanceTV titled “Jonestown: Terror in the Jungle,” which recounts in great detail the deadliest day for Americans before the 9/11 terrorist attacks.

The documentary is executive produced by Oscar-winning actor Leonardo DiCaprio and is based on the bestselling book by investigative journalist Jeff Guinn titled “The Road to Jonestown.” It features unreleased recordings and photographs taken by People’s Temple members, as well as interviews with survivors.

Stephan told Fox News the journey to reach a point of forgiveness was a long, grueling one.

Stephan Jones

Stephan Jones (Raymond Liu/SundanceTV)

JONESTOWN SURVIVOR TELLS ALL

“Many years ago, I was asked by an interviewer, ‘How could you ever be proud of your father?’ he recalled. "And up to that point, I thought I still hated him. And I think it might have had something to do with my first daughter having just been born. She broke into my heart like nobody else could and what came tumbling out of my mouth without thought was, ‘I don’t have to be proud of him. I just have to love him and forgive him.’ I was with [my brother Jim] at the time and his mouth was agape when I said it.

“But I knew when those words came out of my mouth that they were true. I didn’t know how they were true, I didn’t know how I would do it, and it took me years to get there. And I don’t use the word forgive because who the hell am I to forgive anybody?”

On the day of the massacre, the San Francisco Gate previously reported, the brothers were in Georgetown, 150 miles away from Jonestown, for a basketball tournament.

Jim received a phone call from Jones, ordering the Temple members in the Georgetown compound to commit "revolutionary suicide." After pleading with his father, Jim and his teammates rushed to the U.S. Embassy, hoping they could get authorities to stop the horrific slaughter. However, no one at the embassy would open the doors.

Jim Jones Jr.

Jim Jones Jr. (Raymond Liu/SundanceTV)

It wouldn’t be until the following day when Guyanese troops were sent to Jonestown and discovered the carnage. Jim’s pregnant wife was among the dead and at least 300 of the victims were children. Jones, who was 47, was found dead from a gunshot wound to the head. Their mother had died too.

Before the deadly ritual, Congressman Leo Ryan and several newsmen had come to investigate the remote settlement, only to be assassinated by Jones’ followers.

Jim shared he felt a duty to attend the ongoing funerals.

“I remember being at one funeral,” he recalled. “… I remember one mother pulling out a gun and pointing it at me and saying, ‘Why should you be alive if my daughter’s not.’ And I remember looking at her going, ‘I lost everything. Losing my life is not going to be anything different.'”

People's Temple leader Jim Jones.

People's Temple leader Jim Jones. (Courtesy of SundanceTV)

Jones, a charismatic preacher, first opened the People’s Temple in the mid-1950s in Indianapolis. By the early ‘70s, Jones and his family relocated their headquarters to San Francisco where his popularity grew. Jones’ message of social justice and a racially integrated congregation attracted a diverse group of followers, many of them African-American.

Stephan said that growing up, he did learn some positive lessons from his father.

“There was a lot of good in my father,” he explained. “I mean, people were attracted to him for a good reason. I think he was sick from a very early age, but he tapped into something very real… So my father, more than anyone, taught me that it was OK for a man to be vulnerable, for a man to show affection, for a man to show emotion. Those are gifts that I’ll cherish always. My father preached tolerance. He preached a lot of truths. He didn’t live them, but he preached them. And he put us in an environment where we could live them.”

As a child, Jim felt proud to be a member of the Jones family, one that, at the time, was determined to make a difference in the world.

Portrait of Jim Jones and his wife, Marceline Jones seated in front of their adopted children and next to his sister-in-law (right) with her three children, California, 1976.

Portrait of Jim Jones and his wife, Marceline Jones seated in front of their adopted children and next to his sister-in-law (right) with her three children, California, 1976. (Getty)

“I had the best brothers and sisters I could ever have,” he said. “Don’t get me wrong, we fought like brothers and sisters, but the closeness and solidarity between us was better than any bond, because it wasn’t blood. It was a bond of commitment that we were a family… I felt loved. I felt really truly loved.”

But by the ‘70s, news media were beginning to investigate claims made by ex-members of abuse and tyranny within People’s Temple. It reportedly prompted Jones to summon his followers to the promised land of Jonestown where utopia seemingly awaited them.

The brothers shared they witnessed their father become increasingly addicted to pharmaceutical drugs.

“I knew drugs were a problem with my father,” said Stephan. “In Jonestown, he [would] come on the loudspeaker and his speech was slurred. It was obvious to everyone that he was on something… I watched him… get shot up with something. He said it was B12 and I know that was not B12. He could barely speak to me after that happened. But dad… was using drugs to wake up and using drugs to go to sleep and feel better about himself for a long time.”

The men have been haunted by the deaths of those who perished in Jonestown. Today they have found new lives as hands-on parents, which encouraged them to overcome survivor’s guilt over the years. They’re thankful to be alive for their children.

“I wanted to get better,” said Stephan. “And when I was ready to do the work that was necessary for that to happen, people showed up in my life and helped me do that… No one has done that better than my daughters. They are so tuned into me and they’re so sensitive to me. When I am going dark, they call me on it immediately and I’m grateful… Life is good now, but it wasn’t for many years.”

Jim said he hopes the documentary will encourage viewers to not only remember the dead, but also those who made it through. The former members who could never forget their terrifying past, yet are willing to openly share the lessons that can be learned from it.

“I want to recognize the survivors,” he said. “I don’t want to revise the truth, I want to state the truth. These people didn’t commit revolutionary suicide. What they did was they got up for 40 years every day and lived.”

Jim Jones in Jonestown.

Jim Jones in Jonestown.

"Jonestown: Terror in the Jungle" airs Nov. 17 at 9 p.m. on SundanceTV.