From: 20th Century Danny Boy, 1939 Letter from Grace Everett, Re: Bill Everett & Amazing Man.
This ebay page may or may not be available. According to it:
The letter is from Grace Everett the wife of Bill "William" Everett the creator of Amazing Man, Prince Namor the Sub-Mariner and Daredevil. This letter is dated and stamped by the City of New York March 1, 9:30PM, 1939 which was 6 months before the first Prince Namor the Sub-Mariner can out, which in a way is talked about in this letter.
The addressee is "Mrs. A. Carleton Potter, 1 Potter Park, Cambridge, Massachusetts."