I am sorry to hear of the passing of your relative. When you say "gift", I'm assuming that you acquired ownership of the bond upon the your relative's death. The recommended reference is : https://www.irs.gov/pub/irs-pdf/p550.pdf (The 2017 version of the Pub 550 is latest available today, however, I'm not aware of modifications for this topic.)
Page 9 of the current Pub 550 states, "The manner of reporting interest income on Series E, Series EE, or Series I bonds, after the death of the owner (decedent), depends on the accounting and income-reporting methods previously used by the decedent." Examples are provided in the publication. For some cases, the executor of the estate pays taxes as part of the estate taxes. And if the executor did not pay taxes on the bond from an estate tax return, then it appears that you would pay the taxes--most commonly, when you redeem the bond.
