In Ghaibat Nomani: It is narrated from Ali bin Ahmad from Ubaidullah bin Musa from Abdullah bin Hammad from Ibrahim bin Abdullah bin Alaa from his father from Imam Ja'far Sadiq (a.s.) that he said: "Amirul Momineen (a.s.) informed of some things that would happen after him until the appearance of the Qaim.

Imam Husain (a.s.) asked him: "O Amirul Momineen, when does Allah clear the world from the unjust people?"

Amirul Momineen (a.s.) said: "Allah does not clear the world from the unjust until the sacred blood is shed." He mentioned the story of the Umayyads and the Abbasids in a long tradition then he said: "When the Qaim rises in Khurasan, defeats Kufa and the two nations, passes the island of Bani Kawan, and another revolter from us rises in Jeelan, who will be supported by the people of Aabir and Daylaman, then the banners of the Turks will rise in different countries to support my son (the Qaim). Then some things will happen here and there. Basra will be destroyed and the Amir of the Amirs will rule in Egypt."

He told a long story and then said: "When armies get ready, different leaders rise, revolters rebel and unbelievers perish then the EXPECTED QAIM AND THE UNKNOWN IMAM WILL APPEAR WITH HONOR AND VIRTUE.

O Husain, he is your descendant, who has no like at all. He will appear between the two corners (of the Kaaba) in ragged cloths. He will rule over all the peoples and will clear the world of every evil. Blessed is he, who lives until his (the Qaim's) age and enjoys his rule."
{Bihar Al Anwar - The Promised Mahdi, page132, hadith 104}

Approx. 300 million Shias today know about Imam Al-Mahdi (a.s) and millions of sunni`s too,, Muhammad son of Al Hasan (ajf) he is known but for the unknown Imam, who could he be?

AlGaiba Al Sheikh AlToosi p.138-139 "The Prophet of Allah (pbuhap) said: "Me and 12 of my sons and you are O Ali the balance of this earth, meaning its pegs and the mountains"

And 12 of my sons:

First son: Imam Hasan. Second son: Imam Hussain. Third son: Imam Ali ibn Hussein. Forth son: Imam Muhammad ibn Ali. Fifth son: Imam Jafar ibn Muhammad. Sixth son: Imam Musa ibn Jafar. Seventh son: Imam Ali ibn Musa. Eighth son: Imam Muhammad ibn Ali. Ninth son: Imam Ali ibn Muhammad. Tenth son: Imam Hasan ibn Ali. Eleventh son: Imam Muhammad ibn Hassan. 12th son: Ahmad. (pbut)

Refer to the Will of Muhammad (pbuhap).

And peace and blessings on your guardian (Imam Al Mahdi),and those who bear your promise and the Imams from his sons”
{Bihar Al Anwar. v.99, p.114, v.52, p.20}

The Imams from the sons of Imam Al Mahdi (pbuh) is in reference to a rank that will be earned and achieved not that they are the 12 Imams of the Ahl Al Bayt (pbut) except Imam Ahmed Al Hasan (pbuh) who is Imam Hussain in the return.

And an example of reaching a rank of Imamat can be seen in this verse where Abraham (pbuh) as a Prophet reached this rank:

And [mention, O Muhammad], when Abraham was tried by his Lord with commands and he fulfilled them. [Allah] said, "Indeed, I will make you an imam for the people. (Quran 2:124)

As we know from Imam Ahmed Al Hasan (pbuh) many of the Mahdi`s after the first Mahdi, are Prophets (pbut) and so therefore like Prophet Abraham (pbuh), they would achieve a rank of Imamat.

O Allah send your peace and blessings upon Mohammed and the family of Mohammed the Imams and the Mahdis

Salam, À ceux qui ne jurent que par le Coran… […]

A- Nom nouveau du Mahdi.

Salam, Le Coran et Al-Kawthar sont reliés. A-1[…]