The realisation of 12th Imam has never been in the world of corporeal existence.Thou hast asked the detail in relation to the 12th Imam. The realisation of this entity has never been in the world of corporeal existence. Rather His holiness the 12th Imam has always been in the realm of the unseen. He had never a realization in the world of physicality rather some of the leaders of the Shi'ihs at that time in the past, merely to protect the weak souls considered it expedient to describe that Personage Who is present in the realm of the unseen in this manner. Their descriptions were such that one could almost imagine that He is in the realm of physicality. For the world of existence in its totality is one world. "It is only unseen in relation to you and it is only visible in relation to you." All this was their consideration, their thought their expedience. There is a couplet composed by Ibn Hajar in this regard in his Sawaa'iq Muharriqah (Sunni book written against Shi'is)
How can the Sardab [=the Cellar in Samarra Iraq] give birth to a human child?
God forgive your thoughts! for you have truly found a third to the mythical twin of the phoenix and the mythical giant.
In sum if you refer to all the traditions in this regard and if you exert the utmost careful study you will conclude that this peerless being the 12th Imam has never existed in the world of physical existence.
MuhAdarat Volume 2 page 833 Dar khusus e Imam e Thaani 'ashar.