Rule reminder
After superlative relative clauses (il più... che, il meno... che) and after restrictive expressions (l'unico che, il solo che, il primo che, l'ultimo che), the subjunctive is used. These constructions imply a judgment or evaluation where the speaker's perspective frames the statement as opinion rather than objective fact.
You are the only one who knows the truth. Choose the correct form: 'Sei il solo che _____ la verità.'