Hi. I've done some research on this as I've known about it for a while. I have lived in France. As he says in the video it is definitely true that Our Lady told Maximin Giraud and Melanie Calvert that Louis XVII was still alive. For some reason the Bishop and the Vatican kept it secret (as they have the third secret of Fatima) as it is politically explosive! The Great Monarch will be a direct descendant of Louis XVI and Marie Antionette.
Maximin visited the Comte de Chambord with a message from Our Lady. The Holy Virgin told the Comte via Maximin that he must not accept the Throne of France as Louis XVII was still alive.
The Comte de Chambord's Secretary made a note of the Conversation.
Apparently Marie Julie Jahenny also referred to the survival of Louis XVII.
Melanie Calvert at some juncture told her Confessor the Abbe Combe that the "Naundorf"family descended from Louis XVII. It's written in the Abbe's book "
"Journal de l'abbé Combe. Dernières années de Soeur Marie de la Croix, bergère de la Salette"

A 19th century French Mystic called Thomas Martin has a lot of interesting information on the subject of the survival of the Dauphin, Louis XVII . Thomas Martin is known to have received apparitions of the Archangel St Raphael. The circumstances of The apparitions and the warnings sent from Heaven re the Usurpation of the Throne are included in a chapter in this book. He was ordered to go to tell the King (Louis XVIII) to vacate the Throne.

Storied Italy, : Hugh Fraser : Free Download, Borrow, and Streaming : Internet Archive

Interesting news article from 1916