King Charles III, Queen Camilla and the Prince of Wales will be among the visitors to Aberfan on Wednesday to mark 60 years since the coal waste tip collapse in the former mining village that killed 144 children and adults.
A prayer and moment of silence will take place and a male voice choir formed after the disaster is set to perform.
The royals will also join survivors, bereaved parents and other members of the community to mark the anniversary, who will share their personal reflections.
On 21 October 1966, 116 children and 28 adults were killed when the colliery spoil tip collapsed and engulfed a primary school and surrounding houses.
The King, Queen and Prince William will visit the Aberfan Memorial Garden, built on the site of the destroyed Pantglas school, as well as the community centre where they will meet retired emergency service workers who helped in the response.
They will also look at an exhibition that shows the huge scale of the rescue effort, and spend time with former pupils at Pantglas school, siblings of those who died and members of the Aberfan Wives – a support group for mothers who lost children in the disaster.