Nsc taxabililty

Hello, My grandfather had purchased NSC in March 2010 of Rs.25000/- in the joint name of himself along with me.Now in March2016,it got matured and in May2016,I got Rs,41050 as maturity amount.My grandfather died in 2011.Now I want to know about the taxability of NSC proceeds and I had never filed ROI bcoz the income was below the taxable limit.Please advice me regarding the taxability and in which A.Y.. I shall be very thankful to you.