Are there any significant discoveries that were discovered by accident?

The man below is Donald Lewis.

He would often sit and read after long days. Unfortunately for him, one night while he was reading a car plowed into his living room and killing him instantly. The driver was determined to have been under the influence of alcohol and marijuana. When going through the his belongings his family found several pictures of him with other families. Donald hadn't just been living a double life, he was living multiple lives.

No one even suspected that Donald wasn't who he said he was. He had bills for several different aliases, several passports, and multiple licenses. After going through his belongings they found out Donald had three wives at the time of his death and over fourteen children. Two of which had been married to each other unaware of their father's secrets making them siblings.