A 14-year-old boy who died had been bullied at school, his father has claimed.
Bradley John, from Ammanford, died in hospital on Wednesday after emergency services attended St John Lloyd School in Llanelli.
His father Byron John has alleged Bradley was bullied.
Carmarthenshire Council, which runs the school in partnership with the Diocese of Menevia, said it was "inappropriate to speculate on the circumstances".
Dyfed-Powys Police said it was not treating the death as suspicious but was investigating.
Mr John said his son, who had Attention Deficit Hyperactive Disorder (ADHD), "was so loved...if he could have seen that, we could have prevented this".
He said "bullying at any level shouldn't ever happen".
My best friend
Mr John added: "Whatever we do now we will never see him, laugh with him, get mad at him.
"He was my best friend, my mate, nothing's going to bring him back."
Mr John claimed Bradley had also been bullied at comprehensive school Ysgol Dyffryn Aman before moving to St John Lloyd.
A Ysgol Dyffryn Aman spokesman said: "During his short time at the school, he was encouraged to reach his full potential. We are very saddened to hear of Bradley's death."
Mr John previously paid tribute to "accomplished horse rider" Bradley, saying: "We as a family are devastated to lose Bradley. He was such a charismatic, wonderful and dearly loved individual."
Carmarthenshire Council said Bradley death's was a "tragic incident". The Diocese of Menevia has been approached for comment.