12-13 TAMUZ. The 12th of TAMUZ is the Frierdike (previous) Rebbe's birthday. He was born in 5640/1880. On this date in 5687/1927 he was freed finally from his incarceration and exile in Soviet Russia. He declared this day a Yom Tov (holiday) for the victory of Yiddishkeit over it's oppressors.
17 TAMUZ. One of the four fasts that commemorate the serie sof events that led to the distruction of the first and second beis Hamikdash and the exiling of Jews from the holy land.
The three weeks
The three weeks. The period of mourning between the fasts of 17 Tamuz and 9 Menachem Av that mark the time of the Beis Hamikdash's destruction.