According to Jewish Tradition, the Mashiach is born on Tisha B’Av.  According to the RAMBAM, it is the Mashiach who will lead the Jewish People in the building of the Third Beit HaMikdash, that is never to be destroyed.

All of the Prophets prophesied concerning the “Acharit HaYamim,” the “End-of-Days,” Yeshayahu perhaps most beautifully:

“And it shall come to pass in the End-of-Days,
That the mountain of the L-rd’s House shall be established
As the tops of the mountains,
And shall be exalted above the hills;
And all nations shall flow into it.”

“And many peoples shall go and say:
’Come, and let us go up to the mountain of the L-rd,
To the house of the G-d of Jacob;
And He will teach us of His ways.’
For out of Zion shall go forth the Law,
And the word of G-d from Jerusalem.”

Yeshayahu (2:2-3)

and also,

“Even them will I bring to My holy mountain,
And make them joyful in My house of prayer;
Their burnt-offerings and their sacrifices
Shall be acceptable upon My altar;
For My house shall be called
A house of prayer for all peoples.”

Yeshayahu (56:7)

The Tisha B'Av Index