Frank believed his direct ancestor was Black Jack Randall. It turned out that wasn’t the case in the world of Outlander. How are they related?
When Outlander started, we went into the series believing that Black Jack Randall was the multiple-great-grandfather of Frank Randall. There was no reason to believe otherwise. Frank had researched his family tree and made it back to Jonathan Randall marrying Mary Hawkins.
It turned out that Frank was wrong. However, it’s easy to understand how he was mistaken. Nobody would have known the difference except for those willing to do some math and follow Mary’s whereabouts in the 18th century.
One of the common Outlander questions is how the two were related then.
Black Jack’s brother was Frank’s direct ancestor in Outlander
Black Jack and Frank Randall are related but not directly. This was something Claire only learned because she was in the past and because she got to know Mary Hawkins. She thought all the way up to getting back to Scotland just before Culloden that Black Jack Randall and Mary Hawkins needed to end up together.
It turned out that Mary was in a relationship with Jack’s brother, Alex. He was actually the father of Mary’s baby. However, Alex died ill, and rather than leave Mary destitute, he asked for his brother, Jonathan, to marry Mary.
Claire realized that Mary marrying Black Jack Randall would be a good thing for her after Culloden. Randall was going to die, anyway. His death would mean Mary would be left with his pension and name. She had a fighting chance in life, but it meant the world had to believe that her baby was Jonathan’s and not Alex’s. It was a price worth paying at the time.
So, Black Jack Randall is actually a great-great-however-many-times-uncle of Frank Randall rather than grandfather.