There is a theory, particularly popular amongst Snape and Snily fans, that Snape was truly Harry's biological father instead of James Potter. There are two main variants of this theory. The first is that Lily had a long term affair with Snape, possibly from when they were all in their final ano at Hogwarts together. The segundo is that Lily had a one-night-stand with Snape after arguing with James, which she immediately regretted but which led to Harry's existence.

The first issue with this theory is how strongly Harry resembles James. The only difference in their physical appearance is their...