Rene III wasn't mentioned on the list of kids captured & taken to Canada. Several of these children weren't. I've heard Rene III was the only one mentioned in his mother's will but I don't know how she could've left a will considering she lost everything.
We do know he existed however as a few children are listed in their uncle's will plus they or their spouses or children have been found. Rene III & Agnes Robinson were the parents of David, Mary, Rene IV & Robinson. Rene III & Mary "Polly" Gillespie were the parents of Samuel (LeFors), Judith, George, Gillespie, Gaston, Isabella & Trephanah.