Greater or Lesser Black Backed Gull

This Gull was seen on 10 October 2021 on Caribbean island of St.Kitts. Lesser BBG are seen every couple of years, but Greater BBG have been seen on very rare occasions in some neighboring islands such as Barbuda, Guadeloupe, Barbados, St. Croix etc. but only as a vagrant.

It is important to get a firm ID as it would be the first sighting of a Greater Black Backed Gull in St.Kitts. On another bird ID forum, nearly all posters believe it is a Greater BBG, but because of the location of the sighting so far south of the US, they want to see another known bird next to it to compare sizes, or to see it in flight! However, they all believe it is a Greater Black Backed Gull but are reluctant to confirm 100%. Can anyone give me their expertise on which Gull it is likely to be based on the attached photos? Thanks