Landlord's sister filed a case against me for buying land

Hello,

In 2014, I and my Brother brought land from a landlord. Recently we have received a civil court notice to appear in the court for buying land. And the case is filed by landlords sister in 2013 for her share. The case issue was not told by landlord to me at the time of buying. One better part is I have brought the land, which is transferred by landlords father through registered will.

Please suggest me, how to process this issue.