The Greystone Bastard (naming lore query)

[FJerome]

But aside from that there's definetly something wrong brewing in the Fortemps household, you have to wonder why Edmont didn't even lift a brow when his oldest son offered to put down his sword in the vault while his middle child is still "warm in his coffin" as Lucia says.

Somewhat tangential but do we know for certain that Haurchefant was the middle child or is that something we've all been assuming?