Reuven Kimmelman, "Rabbis Joseph B. Soloveitchik and Abraham Joshua Heschel on Jewish-Christian Relations" in Modern Judaism 24:3 (October 2004), pp. 263-264 n. 7:
R. Shalom Dov-Ber Wolpo (Shemen Sasson me-Haveirekha [Holon, Israel, 5763], p. 186) reports that R. Ephraim Wolf wrote to the Lubavitcher Rebbe that the former president of Israel, Zalmen Shazar, told him that Soloveitchik, whom he met in his hotel in New York City, mentioned that he had met both R. Schneersohn, the future Lubavitcher Rebbe, and Heschel in Berlin. Professor Haym Soloveitchik (telephone conversation, March 16, 2004) told me that his father told him that he only saw the future Rebbe pass by. My wife's uncle, Zvi Kaplan of Jerusalem, told me that R. Yitshak Hutner told him that he was with the future Rav and Rebbe together at a lecture on Maimonides at the university (apparently in 1929). After the lecture, when the professor approached Schneersohn for his opinion, he deferred to Soloveitchik. In any case, in Berlin both Heschel and Soloveitchik maintained relations with R. Hayyim Heller, R. Jehiel Weinberg, and Professor Eugene Mittwoch.
R. Fabian Schoenfeld (telephone conversation, March 21, 2004) recalls seeing Heschel in the 1960s at two of Soloveitchik's yahrzeit lectures for his father in Lamport Auditorium of Yeshiva University. Haym Soloveitchik recalls that in 1962-1963 he saw the two together twice in his father's Yeshiva University apartment and heard of a third meeting from his mother, who was at all three. He also recalled (telephone conversation, June 23, 2004) that R. Heschel consoled R. Soloveitchik in 1967 when he was sitting shiv'ah for his mother in her or his brother's apartment in New York. Heschel's daughter, Professor Susannah Heschel, e-mailed me that she recalls Soloveitchik visiting her father in their home in the mid- or late 1960s and that he paid a shiv'ah call when Heschel died (Shabbat night, December 23, 1972).