The 15-year-old claimed victory at the iconic Kanal Bridge diving competition in Slovenia.
Competitors leap from the town’s bridge, which is 17 metres high, and into the Soca River.
Heslop was the youngest competitor in the event, which has been going since 1988, but was too good for all his rivals.
It was the Plymouth star’s fourth high diving win of the season and followed his success at the WHDF International Cliff Diving Championship in Ponte Brolla last month.
Heslop, who hopes to compete for Wales at next year’s Commonwealth Games, has also enjoyed an impressive year in the pool.
He won a bronze medal in the boys’ B event for Great Britain at the European Junior Championships in Norway, claimed a hat-trick of titles at the British Junior Elite Championships and won a bronze medal at the senior FINA Grand Prix in Madrid.