Yeah, Artoirel is the Eldest (legitimate)Son of Edmont de Fortemps
Let us begin anew, Master Surname. I am Ser Artoirel de Fortemps, eldest son of Count Edmont de Fortemps. You will forgive me my outburst, I hope. I meant no disrespect. I merely consider myself equal to the duties entrusted to me...unlike some.
http://ffxiv.gamerescape.com/wiki/Lo...:Over_the_Wall

Since the writers are such big fans of GoT it's more in line with Robb Stark being many months older than Jon Snow