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Tell me the truth, come on.
Literal
True [possessive-の] thing [object-を] teach [casual request-てよ].
教えてよ ('tell me, come on') uses the casual request form ~てよ — more insistent than ~て alone, softer than ~てくれ. 本当のこと is 'the truth/the real story.' A direct, friendly demand for honesty.