Abraham Lincoln: "Big enough to be inconsistent."

[ELCore]

"Abraham Lincoln was a Southern poor white, of illegitimate birth, poorly educated and unusually ugly, awkward, ill-dressed." (Du Bois)

I see a lot of pushback to the idea of ugliness, but I'm wondering where the notion of illegitimate birth comes from. Surely, there is no doubt that Thomas and Nancy were married long before Abraham's birth. Indeed, he was their second child.