Step 1: Convert letters to position numbers.
D = 4, G = 7, K = 11, P = 16.
Step 2: Find the pattern in differences.
G - D = 3, K - G = 4, P - K = 5. The differences increase by 1 each step, so the next difference = 6.
Step 3: Find the next letter.
16 + 6 = 22, and the 22nd letter of the alphabet is V. \[ \boxed{\text{V}} \]