The unique pink lady has ripened on one side and a perfect line divides the red and green halves.
Wayne Ames, 41, who runs Southsea Fruit and Veg in Portsmouth, Hants, said he has never seen anything like it in eight years as a greengrocer.
The married father of two said: "It looks like two different apples have been welded together.
"For some reason it is completely different colours on the two halves.
"Customers who have come in and seen it have been quite shocked."
Mr Ames is now considering preserving the 125g apple, which he would usually sell for 35 pence.
He added: "It is one of a kind.
"You see the odd funny-shaped potato in this job but in eight years working with fruit I've not come across anything quite like this.
"It's been suggested I should put it in some sort of preservative so I might well do that."
Edited by Amy Willis
