An entire generation was almost wiped out when 150,000 tonnes of coal waste slid down the hillside before engulfing Pantglas Junior School and a row of houses on 21 October 1966 at 9.13am.

Firefighters scrambled through a mountain of black slurry to try and save schoolchildren trapped by the collapse, believed to have been triggered by days of heavy rain. The disaster claimed the lives of 116 children.

The late Queen Elizabeth visited the small mining village eight days after the tragedy. The delay was said to be one of the biggest regrets of her reign.

The King, Queen and Prince of Wales joined survivors and bereaved families in the village on Wednesday, visiting the Aberfan Memorial Garden, which is located on the site of the junior school, and the nearby Aberfan and Merthyr Vale Community Centre.

During his visit, Charles said it had been “profoundly humbling” to hear the testimonies of survivors.

In an address to those gathered for the anniversary, he said: “We have heard stories of heartbreak, but also of heroism. We have heard of the most agonising grief, but also of the most inspiring grace.”

He added: “Throughout all this, and through all the years, your unconquerable spirit has shone all the more brightly for the darkness which it has overcome.

“No one should ever have to bear what you, as a community, have endured, but no one could have borne it with greater strength, resilience, or hope. Please know how deeply we feel with your sorrow, how greatly we admire your strength, and how you will, always, be in our hearts.”

The disaster in Aberfan unfolded following days of heavy rain, when excavated mining debris from the Merthyr Vale Colliery was dislodged and came thundering down the hillside.

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.

Children 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. About half the children from the junior school died in the tragedy, which happened on the last day before half-term.

On Wednesday, a prayer and a moment of silence was held in the memorial garden, where the King and the Prince of Wales laid wreaths, and the Queen placed a posy.