Brothers Kyle and James Smith from the Vale of Glamorgan were both travelling in the same car which crashed in 2005.
Kyle was 16, not wearing a seatbelt, thrown from the vehicle and died.
James was 15, wearing a seatbelt and survived.
Their mother Angie Smith says she has "no doubt" that she would have lost both boys, had James not been wearing a seatbelt.
More top news
Jeremy Corbyn will be the main speaker at a Welsh Labour conference coming to terms with Carwyn Jone's announcement of his departure
Any heavy showers will clear away northeastwards through late evening.
The Scarlets were comprehensively beaten 38-16 by Leinster in Dublin.