Pre emption

Int the year 2008 half undivided portion of my joint property was sold by my co shareer without any notice or my consent to a third party . So then i did not allow him to enter into the property. Then he filed one case that is suit for eviction sectkon 6. I lost the case in howrah court by the judgement that he should be allowed to stay in the property even though it is undivided property in the year 2013.then i challenged that in the high court but high court also remains the same judgement now he is in room but i dont want to loose that half undivided portion and without partion he claiming the entire ground floor as court has given him the possession in that said ground floor as it was mentioned in the section 6 case's suit property but in his sale deed there is no demarcation that which portion he bought as it is 2 storied building so now with the help of this judgement he is trying to bypass the partition.now my question is is there any provision by which i can claim or get that undivided 50% share of the property because i lost the time to file a suit for pre emption but i dont want to loose that portion at any cost so pls advice me or help what can i do to get that still undivided share of that property and my co shareer was my mothers uncle as this property belongs to my mothers father and uncle as we have already a undivided half share of my grandfathers.