Conjoined apples

How often does this happen? I think this is my first time seeing this.

I've seen tomatoes like that, but not apples and I have 3 apple trees.

I have some conjoined peaches, will take a picture if they haven’t been blown off by the recent heavy winds.

Not seen any conjoined apples though.

Here's a conjoined peach, the first I've ever noticed

I have seen a number of varieties of co-joined fruit: apples, peaches, pears, plums, cherries, tomatoes, sugar pie pumpkins, zucchini, raspberries. mulberries, acorns, black walnuts, flowers, mushrooms etc.  Mostly because we were encouraged to look for oddities in nature.

Raised by a biologist mother with input from a biologist maternal grandfather and nutritionalist maternal grandmother, things like this interested my mother (horticulture, ornithology, herpetology) and grandfather (zoologist). (Our father was an engineer and could not be bothered with such "flights of fancy".)  Mother would point them out to us children. She found a set of co-joined frogs on one of our many naturalist foraging expeditions. (in the mid 1960's). I still remember examining it and her releasing it back in to the swampy pond where she found it. She believed it had a right to live out its life, such as it was.

Remembered discussions between the adults (like auditing a graduate level course; we were encouraged to be curious and ask questions) viewed the co-joining process as the twinning process interrupted; like co-joined human and other animal twins. An extremely rare occurrence, if I remember correctly. Plant co-twinning was considered less rare (but still extremely rare, none the less) than animal kingdom twinning where natural abortion (miscarriage) usually takes care of its own.

Christopher Weeks wrote:How often does this happen? I think this is my first time seeing this.

It's a first for me too, although sweet peppers often have another little sweet pepper growing inside the other one. Navel oranges have something similar going on at the blossom end. Strawberries can have convoluted fruit, although not quite like what you have pictured here. Interesting....
Of course, we know that some unfortunate baby twins are born conjoined sometimes, and need a complicated operation to separate them. I have quite a few apple trees and have never seen anything like this. Thanks for the pic!

How does a conjoined fruit occur?
Flowers and fruit are derived from stems, over evolution. As a stem develops a flower, leaves adapt to their position - bracts first (maybe), sepals and often colourful petals, anthers (bearing the microspores (pollen) that'll develop male gametes when they grow down the stigma), finally the carpels bearing the female generating megaspores and topped by style and stigma.
There are tons of variations on this theme. With apples the end of the stem bearing the flower parts extends around and above the carpels, and ultmately swells into an apple.
At any point the stem can branch, just as it sometimes does when a stem divides without needing a bud. Sometimes that's due to a boost of enthusiasm, sometimes interence from insect or something.

So odd, I have never encountered conjoined fruit until the peach in the above photo that is growing on one of my stone grown trees.

I was given some homegrown plums and flatto/donut peaches today and guess what??

Yes, another conjoined peach.

Christopher, what have you done?

I am noticing conjoined vegetables now!

Lovely pair of plums...