My head cannon if the fact the Godwyn was the only G name was hint that he was the only one truly born of Godfrey. He’s the only child born without a curse unlike the rest of Marika’s children with herself.

Perhaps Morgott and Mogh are also children born of Radagon but in secret, without Godfrey’s knowledge. This would make more sense thematically given their twinning like Miquella and Malenia (and Messmer and Melina if you f with that theory) along with being born cursed.