Peter Adriaens (Belgium)
Ies Meulmeester (Netherlands)
Larus cachinnans hybrid XUFH 2CY, November 16 2016, Katwijk, the Netherlands.
Steppenmöwe Larus cachinnans plastic green XUFH. Ringed as pullus on June 09 2015 at Gräbendorfer See, Sachsen, Germany.
Probably some argentatus involved, but michahellis equally likely. We'll wait till it grows older over the years...