The other day I mentioned that I had a double yolk egg, the second in my
life. From the same flat of egs, there was another one this morning so
I gave that one to my wife


I guess they are not that uncommon, about 1 in 1000

http://www.betterhensandgardens.com/...-double-yolks/
Each time we’ve raised young pullets, we’ve seen a few double-yolked
eggs; and we’re seeing quite a few now that the Buckeyes are laying. As
the Golden Buffs, Barred Rocks, and Red Comets got older, they quit
producing any double-yolked eggs – it’ll be interesting to find out
whether the Buckeyes quit as they get older too, or whether they’ll
continue to lay a few (Buckeyes are considered a heavy breed hen).

Double-yolk eggs are not really that rare (about 1 in every 1000);
however, they’re rarely seen today because commercial operations candle
the eggs, separate out the double-yolkers, and sell them to make egg
containing products.