Was looking at the Wikipedia page
Odd page. Long history, but none of the usual headers and structure, and no sources.
Peter got inserted anonymously June 2009 (citing a source, incorrectly), removed, and put back, anonymously again.
Found part of the source
Apparently, 94-year-old Galfrid came over with Rollo the Conqueror.
But he doesn't give parents for Peter, he doesn't say Richard was Peter's son, and I've no idea where he got them from or why he bothers to mention them at all, because he doesn't connect them with his immigrant. The alleged Franklin Pierce connection must be somewhere else.