The 16-year-old could hardly believe his eyes when he looked in the bird's nest and found the huge specimen resting among two ordinary sized eggs.
Measuring an astonishing 3.4in long and weighing 8oz, it dwarfs average sized chickens' eggs, which are about 2.75in and weigh in at just 2oz.
But the schoolboy, who took his GCSEs this summer, has been left baffled as to why the egg is so enormous.
And he was shocked that the free range hen had even managed to force out the eye-wateringly large egg.
Dean from Lymington in the New Forest, Hants, now plans to blow out the yolk of the egg so he can keep the shell as a souvenir.
The youngster, who breeds chickens as a hobby at his grandparents' farm in Sway, Hants, said he made the strange discovery while collecting eggs from his 50 hens.
He said: 'I let the chickens out of their coop as normal in the morning and a few hours later I went round collecting the eggs from their nests.
'Some of the hens nest in our straw barn and when I looked in one of them, I spotted this enormous egg.
'I could hardly believe what I was seeing - it was just so large.
'It was nestled in there with two other normal-sized eggs, so up against them it looked even bigger.
'I can't even begin to think why it's so gigantic and I was quite worried thinking how on earth my hen had managed to even lay such a massive egg.
'At first I thought it might have been two eggs stuck together but soon realised that couldn't be the case because it's perfectly shaped.
'I only breed chickens as a hobby and we share the eggs among family and friends - but if they make a habit of laying them this size, then maybe I should go into business.'
Dean, a keen horserider, immediately took the egg to show his grandparents Edward and Margaret Light, who have bred chickens at Little Acre Farm for decades.
He said the egg, although perfectly formed, is paler in colour and has a thicker shell with a rougher surface than most chickens' eggs.
He added: 'My grandparents were totally blown away as well. In all the years they have been poultry farming, they've never seen anything like it either.
'I got straight on the internet to try to find out why the egg is so large but I can't find any explanation.
'I'll make a hole in either end and try to blow out the yolk so I can keep the egg.
'I wouldn't even dream of eating it - as it's so unusual.
'Someone suggested that it could be a double-yolker, but it's far too big for that. I reckon it must be a five-yolker at that size.'
Dean said he hopes to find a career working with animals.
