James Boyd said he and his wife Maggie never got over the loss of Gemma Louise, a niece of the Irish rugby international and serial paedophile.
A 20-year-old university student, Gemma died by suicide just days before Tweed was sent to jail on child sex abuse charges in 2013.
"Gemma had a lovely, bubbly nature. Everyone loved her," said heartbroken James, a brother-in-law of Tweed.
"But she couldn't come to terms with what happened and what Tweed had done. She just couldn't get past it," he said from his home in Ballymoney, Co. Antrim.
Gemma's mum Maggie was just too upset to speak about the loss of the first-born of their three children.
But her husband James said he decided to speak out this week after taking strength in the testimony of his five nieces, who had waived their right to anonymity to set the record straight.
Tweed (61) died last month in a motorbike accident on the north Antrim coast.
He never faced charges connected to the abuse of Gemma Boyd.
James (48) - whose sister Margaret had married Davy Tweed after meeting him at a wedding - said he wasn't angry with his daughter for her suicide.
"I don't blame Gemma, I blame Davy Tweed," he said.
"Gemma had been attending counselling, but there's only so much they can do.
"I understand that because a few years ago, I had a complete breakdown over this and I ended up losing my job," said James, who had previously worked as a steel erectors manager in the building industry.
James also recalled how he had contacted Tweed when Gemma first told him and his wife that she had been sexually abused by the ex-rugby star.
"I phoned Tweed immediately and told him I believed he had touched my daughter. He was silent for a few seconds and then he asked me to repeat what I'd said. I said it again.
"Tweed told me he'd be up to see me immediately, but of course being the coward he is, he never arrived."
After telling her parents about Tweed's abuse, Gemma reported the matter to the police, but found the whole investigation process too stressful to continue with it.
And James also told how he later confronted Tweed following a chance meeting in a Chinese restaurant in Ballymoney.
"Tweed wasn't long out of jail at the time and I had gone to the restaurant to pick up a meal which had been previously ordered.
"I saw him sitting in the restaurant and he looked at me. He said 'What are you looking at?'
"I said, 'That's an open invitation. I'm looking at a dirty, disgusting excuse for a human being, who really needs his bits cut off'.
"Again, Tweed threatened me, 'I'll be seeing you around the town'," he said
"He was a dirty, disgusting, arrogant excuse for a human being. And I'm not afraid to say it, if I had ever seen him around the town I'd have run him over with my car.
"Tweed was a big thug and a bully. And he was especially a bully with younger people and women and small people. He would never challenge anyone near his own height.
"But he was also good at playing 'Mr Nice'," said James.
The heartbroken dad also explained how difficult it was for his family to come to terms with the loss of their talented young daughter.
"It's just constant sorrow and pain. It has affected us unbelievably. Most of the times, we are just shut down," he said.
James said he and his wife Maggie took no comfort from hearing the abuser of their daughter had died.
"It didn't make any difference to us. Gemma is still dead. We're still not getting our daughter back. Davy Tweed devastated our lives. He ruined every part of it," he said.
James also spoke about the ongoing effect the horror of Gemma's death had on the entire family unit.
"Last month, the twins became 21. They were only 13 when we lost Gemma. We tried our best to shield them, but they've seen me break. Your children shouldn't see that.
"I cried for four days. I wouldn't leave the house. I wouldn't leave the bedroom. I actually had a breakdown."
James said that at one stage he became so overwhelmed with depression he even contemplated suicide.
"The only thing that kept me going was my wife and children and knowing that Davy Tweed was still alive. I knew I couldn't leave this earth while he was still walking it," said James.
James looked back on the early signs which eventually lead to his daughter's death at the age of 20.
"We would hear Gemma crying at night and to tell you the truth, we wondered if she was self-harming. But then eventually she told us what was wrong."
He added: "But Gemma just couldn't get past it. The only reason she was in that frame of mind was because of Davy Tweed," he insisted.
James and Maggie kept a close watch on their daughter - who was studying forensic criminology at Queen's University - and they believed she was finally coming to terms with what happened.
"Even the weekend she did it, we thought, 'She's maybe turning a corner'.
"Gemma loved life. She was doing well at university. She got her driving licence so as she could drive up and down. And she thought she would maybe get a job with the police."
James also spoke of how his daughter's death still plays permanently on his mind.
"Gemma comes into my mind first thing in the morning, and before I go to bed at night she's the last person I speak to.
"I often wonder if Gemma would have had a child of her own.
"I visit her grave several times a week and that helps me, but there's nothing I can do to help Gemma.
"If I don't go to the grave I feel something is missing," he said.
He added: "I'm just glad that dirty bugger David Tweed wasn't buried in the same cemetery."
James urged anyone suffering at the hand of a sex abuser to seek help.
"And if by me speaking out it prevents just one person from going down the same road as Gemma, then it will have been worth it," he said.
If you have been affected by any of the issues featured in this article you can contact Women's Aid national 24-Hour helpline at 1800 341 900 at any time of day or night.
The Women's Aid helpline offers confidential information, support and understanding to women who are being abused by current or former boyfriends, partners or husbands. Also, go to
The service also supports family members, friends, and professionals who have concerns about a person, they know or are working with, who might be experiencing domestic violence and abuse.