Survivors of the Aberfan disaster, which killed 116 children and 28 adults, wept as they observed a minute's silence on the 50th anniversary of the tragedy.
About 1,000 people attended a memorial service in the Welsh village's cemetery - the final resting place of those who perished that fateful day on October 21 1966.
Those rescued from the debris of Pantglas Junior School laid floral wreaths in tribute to their tragic classmates as the tight-knit community turned out in force to pay their respects.
The emotional service, attended by Wales' First Minister Carwyn Jones, came ahead of an official visit by the Prince of Wales on Friday.
A minute's silence was also held across the country, with shopping centres, schools, hospitals and law courts coming to a standstill at 9.15am - the time disaster struck.
One hundred and sixteen children died when 150,000 tonnes of coal waste slid down a hillside before smashing into Pantglas Junior School, Aberfan, on October 21 1966. Twenty-eight adults also lost their lives.
Charles will unveil a plaque in memory of the victims of the disaster and sign a book of remembrance, after visiting the Aberfan Memorial Garden on the site of Pantglas School.
Mr Jones said the men, women and schoolchildren who lost their lives should never be forgotten.
"It is a truly heartbreaking moment in our history and no-one who learns about the disaster can fail to be profoundly moved by it," he added.
The disaster unfolded, following days of heavy rain, when excavated mining debris from the Merthyr Vale Colliery was dislodged and came thundering down the hillside on a foggy October morning.
The waste material had been piled high on the side of Mynydd Merthyr - above Aberfan - for years, even though there were numerous underground springs below.
Youngsters in Pantglas Junior School were just getting ready for lessons when 1.5 million cubic feet of liquefied slurry crashed into the school and a number of nearby houses with a tsunami-like force.
Survivor Jeff Edwards said the events of that day had stayed with him and his fellow classmates all their lives.
For two hours the eight-year-old was pinned next to a dead girl from his class, with her head next to his face.
He said: "What we've all experienced are classic symptoms of post-traumatic stress disorder. There's no doubt it has affected me on a daily basis.
"I still have nightmares and sometimes suffer from deep bouts of depression."
The tragedy was all the more bitter to deal with given that coal bosses had been warned about "flowslides" prior to the disaster, and despite a 76-day public inquiry, no-one ever faced prosecution or even lost their job.
Insult was added to injury when a protracted row about removing other coal tips saw frustrated locals left with no choice but to take £150,000 out of a memorial fund to pay for the clean-up bill. The money was eventually returned, but only after decades of campaigning.
Plaid Cymru's leader Leanne Wood said the events before and after the disaster had changed the close-knit community forever.
She said: "The lives of an entire generation in the village were extinguished before they reached their prime.
"A whole generation of adults and grandparents were denied the chance to see their children grow up."
She added: "They endured unimaginable sorrow but maintained a community spirit and built a support network within the village which helped get each other through their ordeal."
That community spirit will once again come to the fore - and in the glare of the world's media - on the 50th anniversary.
Services of remembrance will take place in a number of local churches as well as on the site of the old school, which has now been turned into a memorial garden.