When Armand reads the letter at the end, does he gain new knowledge?

One could think that what Armand gains from reading the fragment of letter from his mother is confirmation, if not new insight. Earlier in the story, the narrator refers briefly to Armand's "dark, handsome face." When his son is born and develops, as he grows, a skin tone that is similar to one of the small "quadroon" boys who works in the house, it seems inconceivable that Armand doesn't consider that his own racial heritage could be the source. This is particularly evident when so many of the descriptions of Désirée emphasize her fair skin, gray eyes, and "golden gleam" in her silky brown hair.
If Armand is indeed cognizant that his mother belonged "to the race that is cursed with the brand of slavery" it would help to explain his mistreatment of his slaves. It is an act of self-hatred. Moreover, rejecting his beloved wife and son is an act of self-punishment. And lastly, burning all of Désirée and the baby's belongings enables Armand to keep lying to himself and those who know him about the truth of who he is.

It can be argued that, from Armand's point of view, the knowledge contained in the letter is not new to him. The main reason Armand is burning the letter is because it contains damning evidence about his racial heritage.
Armand is evidently so ashamed of the knowledge in the letter that he feels he must destroy it. His paranoia correlates with his actions earlier in the story, when he rejects Desiree (his wife) for what he considers her "tainted" blood. In the exchange between the couple, Desiree begs for her husband's compassion. However, he refuses to be affected by her pitiful pleadings. Because the baby's skin color appears to match that of typical "quadroons," he is rejected by Armand.
Armand's behavior betrays his hypocrisy. Despite his own biracial heritage, he places blame on Desiree for giving birth to a child of obvious mixed parentage. When Desiree pleads for understanding, he coldly sends her from his home and presence. Armand's behavior, while hypocritical, demonstrates the pervasiveness of Southern racism and its negative effect on society.