This simple image raises a myriad of questions! First of all, Last Secret? This implies there have been MANY secrets! Like his poker shack out in the swamp, or that drug smuggling operation that he was working out of the toyshop, or the many, many elf-rights violations!
Maybe the fact that there is another Santa on the cover has something to do with it. Did Santa have an identical twin who was somehow hidden, lost, or perhaps locked away somewhere?
So many questions!!!