Confused about Tg Antibodies

I had thyroid cancer back in 2009, and all tests done up to this year showed that I had No Antibodies present and that all the thyroid tissue was gone after the radioactive iodine treatment. Suddenly about three months ago I tested positive for Tg antibodies. I thought this was impossible, and I am totally confused how these could occur three years after I had all the thyroid tissue removed from my body. Could someone please explain how this could happen. I"m just totally confused by this, and to be honest my endocrinologist is not sure how this could happen as well. I thought maybe someone else would know. Thanks in advance.