Does anyone have a source for this man, son of Phillippe De Alett and Blanche De Britagne?

There are numerous records belonging to private individuals that support this person, but I cannot find any source material. I am trying to lay out the French connection of Clan Elliott from France to Netherlands to England and America

Unfortunately, it looks like you have come across a common problem where someone (in my own experience in Victorian times) has concocted a pedigree which has then been accepted by many people without bothering to check any source material. It's so annoying, and so widespread.

Do you have confirmed lineage back to your John Elliott?

I had a look on Wikipedia for Phillippe De Alett, who was actually Philip of Artois, on

https://en.wikipedia.org/wiki/Philip_of_Artois

He is the husband of Blanche of Brittany. According to this article, his child born in 1289 was a girl named Joan (Jeanne), who married Gaston, Count of Foix.

There is a well researched and referenced article on the Artois family on

http://fmg.ac/Projects/MedLands/NORTHERN%20FRANCE.htm#_Toc414122945

but the name Alett is not mentioned.

I don't know if you have been in contact with the Elliott Clan Society, but you might find this article useful - they probably have much more information not on line (clan societies tend to be store houses of snippets of information often from early days and tucked away on cards in filing cabinets) - worth a try anyway.

http://www.elliotclan.com/history/early-history-elliot-clan/

Hope this is of some use.