Mike Smith, from St Asaph, has grown the Dragon's Breath chilli with help from Nottingham Trent University.
It has a Scoville scale rating of 2.4 million units of heat, compared to 1.5 million of the current record holder.
Mr Smith said the chilli's heat was "beyond" and could not be eaten, but instead used as an alternative to anaesthetic in third world countries.
Mr Smith has been growing plants for about eight years and the Dragon's Breath chilli was born out of a trial of new plant food developed by Nottingham Trent University which aims to increase the quality and resistance of plants.
Mr Smith said the chilli was grown on a tree about 3ft (0.9m) high.
He said he had not tasted it as it "would not be a pleasant sensation," adding, "the heat is beyond".
Describing his previous experience of tasting hot chillies, he described the heat as "building up and up" about half an hour after biting into them.
"You should use common sense at the end of the day," he said.
Mr Smith suggested the chilli could be used an alternative to anaesthetic in third world countries - which do not have access to or the money for the drug - as the oil from it is capable of numbing the skin.
It could also be useful on people who are allergic to anaesthetic.
Mr Smith is exhibiting at the Chelsea Flower Show and will enter his chilli into the Plant of the Year category.
"It's different and it's all from Wales," he said.
He has applied to Guinness World Records and is currently awaiting confirmation that the chilli is the world's hottest.
The current record is held by The PuckButt Pepper Company in the US for its Smokin Ed's Carolina Reaper, which rates at an average of 1,569,300 Scoville heat units.
A plant grower from Denbighshire has developed what he believes is the world's hottest chilli pepper.