A 15-year-old boy has died suddenly in his sleep during a school trip to Cuba.
Alex Holliday, who was a Year 10 student at Queen Elizabeth's Grammar School in Faversham, Kent, was learning about marine ecology in Havana.
He died in his hotel room during the early hours of Friday following what is believed to have been "a medical episode from which he did not recover".
His family said he was "gentle, kind and always funny and full of life".
They added: "He was adored by his sister Ellie, and indeed by everyone who knew him."
Alex was among 30 students and four staff on the trip, which had been nearing its conclusion. He had been due to return home later on Monday.
Head teacher David Anderson described him as "a quiet and determined young man with a wonderful sense of humour".
"He enjoyed all aspects of school life and was making good academic progress."
Mr Anderson said the teenager's "great passion" was athletics.
"He was a rapidly improving middle-distance runner and his contributions to the school athletics and cross-country teams will be sorely missed," he said.
Alex also trained outside school with the Invicta East Kent Athletic Club, in Canterbury, where he was "seen as a rising star", Mr Anderson added.
The teenager was a keen parkrunner, who had 100 runs under his belt.
Event director at Whitstable junior parkrun, Russell Evans, paid tribute to him on the website.
"I cannot even begin to think what the loss of Alex to first and foremost his family must feel like, but also his many school friends and fellow athletes at Invicta East. The thoughts of us in the Whitstable junior parkrun team are with you all."