Ridoredh de Bretagne, Comte de Nantes et Vannes - Were Ridoredh and his father murdered together?

I notice that Ridoredh's date of death is shown as 12 November 857. This is also the same date on which his father, Erispoë, was murdered by Saloman and Armarchus at the altar of a church in Talensac. Was Ridoredh present at this murder, and was he also killed by them? I cannot find anything telling me this.

Erispoë had only two legitimate children, a son named Conan and a daughter whose name has been lost to history. So nothing that talks about Erispoë mentions Ridoredh, yet he is listed as Ridoredh's father here.