Is it really possible to be "your own grandpa"? 10/16/11
According to a song that numerous entertainers have performed, it is possible to be "your own grandpa", but the explanation is complicated and it depends on accepting certain definitions.
In 1947, Lonzo and Oscar performed "I'm My Own Grandpa", a song about a man who becomes step-father to his step-mother. It's all legal, too. (Wikipedia) (YouTube)
Country music entertainer, Ray Stevens, also performed "I'm My Own Grandpa" (YouTube, with diagram), still available on his 1987 album, Crackin' Up (Amazon)
If you want more help, following the genealogy, this page with interactive lyrics and diagram that may clarify things. (Children of the Shenandoah )