At the time of this writing, "Cari Ddu David" is listed as the mother of four illegitimate children by William ap Thomas, but the evidence for that is coming out of web trees.
Several printed sources do give her as the mother of John Herbert, though.
Wikipedia, for what it's worth, doesn't mention her at all, and attributes William's occasionally mentioned children (Maud, Olivia, Elizabeth, and Thomas) to his wife Gwladys Ddu. John they don't mention.
Unless someone has evidence that Cari is the mother of the occasionally mentioned children, I'm going to move them over to Gwladys.
Also, "Cari Ddu" is, I think, the only name we have (Cari, the Dark-Haired or Dark-Eyed) -- if there is evidence that her father was named David I haven't seen it. If you've got evidence for that, other than the web trees, that would be great.
tagged -- Cari Ddu (the @ function isn't working for me at the moment)