Rav Tzvi Meyer Zilberberg quoted from Seforim Hakedoshim, the following: "As soon as the Second Beis Hamikdash was destroyed, Hashem began preparing the final Geulah and the Third Beis HaMikdash."
Does anyone know which sefer actually says this?
See this article, and especially this quote from the Talmud Yerushalmi:
On the day that the Holy Temple was destroyed, a Jew was plowing his field when his cow suddenly called out. An Arab was passing by and heard the low of the cow. Said the Arab to the Jew: "Son of Judah! Unyoke your cow, free the stake of your plow, for your Holy Temple has now been destroyed."
The cow then lowed a second time. Said the Arab to the Jew: "Son of Judah! Yoke your cow, reset the stake of your plow, for the Redeemer has now been born..."
Said Rabbi Bon: "Do we need to learn this from an Arab? The Torah itself says so. The verse (Isaiah 10:34) predicts, "And the cedar of Lebanon shall be felled by the mighty one." And what is written in the very next verse? "There shall come forth a shoot out of the stem of Yishai"
(Jerusalem Talmud, Berachot 2:4)