Clues for finding the 4th Hidden GA:

Hint for character types: There are no digits (numbers) within this GA code.
Hint for case: There are 4X more uppercase letters than lowercase letters.

1. One letter is the first letter of the 2nd word of the Spanish novel written by Miguel de Cervantes Saavedra. Published in two volumes, in 1605 and 1615. (Novel title is only 2 words.) LOGIC: (This letter is directly before the 3rd character within the GA code.)

2. One letter is the first letter of the second King of the Belgians, born April 9th, 1835 in Brussels. LOGIC: (This letter is not the last character within the GA code.)

3. One letter which is non-uppercase is often confused with the first number of the set of counting numbers and the second number within the set of whole numbers. LOGIC: (This letter is one of the last 3 characters within the GA code.)

4. One letter is the first letter of both the first and last name of the famous American composer and pianist that composed "Rhapsody in Blue", and "Porgy and Bess". LOGIC: (This letter is neither the 4th or 5th character within the GA code.)

5. One letter is the first letter of a marsupial with a pouch and a joey within. LOGIC: (This is the first character within the GA code.)