Weighing in at 181g, this is probably one of the largest chicken eggs ever laid — but wait until you see what's inside of it. And yes, it looks to be genuine — or, at the very least, possible. After you've watched the video, read the explanation below. But watch the video first so you don't spoil the surprise.
According to Alex Williams and verified by New Scientist an egg within an egg is a natural but rare occurence. Occasionally during normal egg formation an egg travels back up the oviduct, meets another egg travelling down, and becomes encased inside the second egg during the shell forming process, thus creating an egg within an egg. It is especially unusual to encounter this phenomenon in a shop-bought egg, because these are routinely candled (a bright light is held up to them to examine the contents), and any irregularities are normally rejected.