Rabbi Yitzhak Dubov, one of the elder Chassidim in the 1950s, always believed that the Rebbe was the Moshiach. On the 7th of Shevat, 5735 (1975), he visited the Rebbe for a private audience to receive a blessing before returning to England. During the audience, he said, “Rebbe, you are the King Moshiach, so reveal yourself!” The Rebbe replied, “I have no obstacles, but...” and did not finish the sentence.
Later, at a Chassidic gathering, Rabbi Dubov explained that the Rebbe was ready to reveal himself as Moshiach, but he wanted the Chassidim to be the ones to bring Moshiach.
It is interesting to note that this was Rabbi Dubov’s last private audience with the Rebbe.