Final answer:
The statement "Mon frère, c'est le meilleur!" is grammatically correct in French.
Step-by-step explanation:
The statement "Mon frère, c'est le meilleur!" is grammatically correct. In French, possessive adjectives (such as "mon" which means "my") agree in gender and number with the noun they modify. Since "frère" (brother) is singular and masculine, the possessive adjective "mon" is correctly used. Additionally, the verb "est" (is) agrees with the subject "mon frère".
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