Strange unusual white tail-shaker


🦉 The white wagtail (Motacilla alba)

📚 Motacilla lat .: mōto, mōtare move continuously, -cilla tail (cilla like a tail -
only in ornithology, erroneous established name)
📚 alba (lat.) white

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Seriously, take a look at this wagtail. There's something wrong with her, isn't there?
I asked the experts, and no one could answer me. They say that maybe this is a hybrid, no one knows. Pay attention to the specks under the tail and wing tips. And the spot on the right side of the muzzle is especially prominent.
I tried to search for answers in google, and found one scientific paper regarding the hybridization of these birds. I read it, but alas, in this work hybrids between subspecies of the white wagtail were described. And here is something completely different.

I also saw a couple of suggestions that it is extremely rare that there are hybrids between the white and The grey wagtail (Motacilla cinerea). And I immediately remembered that not far from this place, literally 100 meters away, I saw grey wagtail in the spring. Is this really a hybrid?