Video report by ITV News Presenter Mary Nightingale
The evening of October 21, 1966 was the first night Denise Morgan went to bed without her nine-year-old sister Annette.
"My sister and I shared a bed together, shared a room together," she told ITV News presenter Mary Nightingale as she recalled the close of what became known as Wales' darkest day.
"That first night that she wasn't in that bed with me ... I didn't know at that point that she had died."
Soon Denise learned her younger sibling was among the 116 children who lost their lives, along with 28 adults, on the day Pantglas Junior School was buried by the 150,000-tonne coal rush in the village of Aberfan.
"From then on in I felt an unbelievable grief," Denise said.
The then-11-year-old would repeatedly question "how am I still alive and she's not" as she struggled to come to terms with accepting Annette had died.
"My mother would say I'd be looking for her in the room," she said. "I'd be having nightmares and shouting to my mother, 'I can't breathe, I can't breathe.'"
As Aberfan pauses to mark the 50th anniversary of the tragedy, Denise remembered how the happy village she had grown up in changed indelibly after the disaster.
"You'd be afraid to be out there playing, laughing, joking. There was a silence in the street," she said.
Denise said it left a "massive gap in our street and in the whole village" and forced her to grow up "overnight" to support her family.
"I felt I needed to be there for the younger brother and sisters, because I could see my parents, my mother in particular, crumbling," she said.
"For a long time after she put down Annette's place setting at the table ... it was almost like a source of comfort to her."
Denise later became a member of the Aberfan Young Wives Club that was set up after the disaster.
Half a century after a tragedy she still remembers "as if it's yesterday", she said Annette has always remained in the family's thoughts with so many questions about her life left unanswered.
"It's her birthday now coming up," Denise said. "She'll be 60, so everyone's thinking now what would she be like? What would she be doing? Would she be married? What would her job have been? Would she have children of her own?
"It doesn't take the 50th anniversary, we've had 50 years of this. Every time there's a family occasion, every time there's been a landmark birthday for her, you just think 'well what would her life be like now?'"