Tributes have poured in for the "gentle soul" who died after becoming suddenly unwell at his school gym.
Ademidun Adeleke (15), affectionately known as Ade, was a popular third-year student at Scoil Mhuire in Clane, Co Kildare.
He was rushed to Crumlin Children's Hospital in Dublin following the incident on Tuesday.
Tragically, he was pronounced dead a short time later.
Naas Athletic Club led tributes to their committed member and cancelled all training last night as a mark of respect.
Speaking to the Herald, the teen's coach Brian Dowling said that Ade had a very promising year ahead of him.
"Ade was a lovely young man, quiet and shy, who loved his athletics," he said.
"He was part of a mixed training group, who are shocked and very upset at his passing.
"The club is following [Athletics Ireland's] serious incident protocols to help deal with the effects of his sudden death.
"He has trained hard over the past two years and was in line for a merit award this year for his progress. He was also expected to compete in Kildare County Indoor Championships in January. He will be missed."
Gardai have confirmed that they are investigating the tragedy as a sudden death and foul play is not suspected.
A post-mortem will be carried out to determine the cause of death.
A statement posted on the club's Facebook page read: "It is with deep sadness and shock that we have learned of the passing of Ade Adeleke, one of our young athletes.
"A gentle soul who loved athletics and his training with coach Brian [Dowling].
"He will be very much missed by his fellow athletes and coaches. Our thoughts and prayers are with his family and friends at this very sad time. May he rest in peace."
The tragedy, which happened just days after students returned to school from the summer break, has left the school and wider community devastated.
Principal Padraig Nolan described Ade as an excellent student.
"He was always on time for school and always did his work to the best of his ability," he told the Herald yesterday.
"He loved his sport, in particular athletics, and was a big Liverpool fan. The whole school is in shock."
His death prompted the school to put its critical incident plan in place and school psychologists are on hand to provide counselling to students if needed, Mr Nolan added.
While the results of the post-mortem will confirm the exact cause of Ade's death, a source told the Herald that one cause being considered is sudden cardiac arrest.
Around 100 otherwise fit and healthy people under the age of 35 die from sudden death syndrome (SDS) in Ireland each year.
According to Cardiac Risk in the Young (CRY) charity, young, fit people who have an underlying and undetected cardiac abnormality may seem perfectly healthy just hours before they suffer a cardiac arrest, often while engaging in sport.