Step 1: Understanding the Concept:
The Triple Entente was a major alliance formed before World War I as a counter-balance to the Triple Alliance.
Step 2: Detailed Explanation:
The Triple Entente (1907) consisted of three core signatories:
1. France
2. Russia
3. England (Great Britain)
While Japan was an ally of Great Britain and joined World War I on the side of the Entente powers, it was not an original core signatory of the Triple Entente treaty itself.
Step 3: Final Answer:
Japan is the odd one out among the core signatories.
Hence, the correct option is (C).