There are nine days between Yud Kislev and Yud-Tes Kislev. On Yud Kislev we celebrate the liberation of the Mitteler Rebbe, the 2nd Lubbavitcher Rebbe, which also marks the date of his birth and yahrzeit (9th of Kislev). Yud-Tes Kislev is the liberation of the Alter Rebbe, the 1st Rebbe, as well as the yahrzeit of his teacher, the Maggid of Mezeritch.
When the Previous Rebbe had his bar mitzvah, his father, the Rebbe Rashab, made a seven-day celebration like that of a wedding (sheva brachos). Therefore, perhaps we can say as follows, "Gimmel Tammuz marks the wedding of a chassid, and Yud-Beis/Yud-Gimmel Tammuz is the sheva brachos."