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Triona McNabb was 34 years old when she died in hospital on 27 February 2017.
A post-mortem examination found a blockage in her bowel.
Her family struggled to come to terms with what happened in the aftermath of her death.
Triona was the youngest of four sisters – Edel, Maeveen and Cathy, from County Tyrone.
They found themselves acting as a support for the wider family circle but realised there was little support specifically for bereaved adult siblings.
Speaking to BBC News NI, Triona’s sister Maeveen said: “Losing a sister or a brother, is very much like losing a part of yourself, because they are the only people that are there from the very beginning.
“Adult siblings are often the forgotten mourners and the ones that have to be strong for everyone else, so I decided I wanted to do something about that.”
With the help of her two others sisters, Maeveen created the Sibling Grief Club.
Its purpose is to connect other bereaved adult siblings and create a safe space for them to share their stories, as well as signpost them to grief professionals.
“So many people have been reaching out and being able to share those stories has been amazing,” she said.
“It’s part of Triona’s legacy and her spirit lives on through this club that can help others, and that means the world to us.”
Video journalist: Niall McCracken Published15 August Section BBC News