Answer: Because fruits are, botanically speaking, structures that contain seeds, it will be a challenge. Even "seedless" fruits usually have rudimentary seeds which, due to breeding, don't mature and are therefore usually quite soft and small.
You've probably already considered fruits with large seeds that can be removed, such as cherries, peaches, pears, plums, etc. Blueberries, gooseberries, currents, and cranberries all have seeds inside, but the seeds are small. I suggest he ask his doctor if these would be OK to eat. Does he enjoy melons? Another possibility is rhubarb, which is not, technically, a fruit. Or perhaps he can eat products from which the seeds have been strained out, such as seedless raspberry jam.
There are "seedless" tomatoes, but I'd be cautious because they, too, contain some seeds. You can, of course, manually remove the seeds on peppers (though you'd have to be really diligent to remove them all).
I hope this helps. Again, I suggest you check with his doctor before trying anything new.
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