Hybrid?

My friend Dimiter Georgiev, from Bulgaria, is sending this set of photos at Varna Lake.

This gull shows features both from michahellis and cachinnans, so I cannot rule out a hybrid. 

Important features supporting michahellis:

* Pale iris
* P10 pattern

And those supporting cachinnans:

* Half rear neck collar
* Long legs
* Jizz on the first photo

Bill is somewhat confusing, showing no hints towards micha or cachi IMO.

Opinions would be appreciated.