She's his great-great-great-great-great-great-great grand mummy.
While there was no gravestone to identify her, and her coffin was unmarked, she was buried in front of the altar, which is a symbol of great importance, and was wearing good quality clothes. The high concentration of mercury in her body is what preserved it enough for it to be exhumed and studied.
Her body was most recently uncovered in 1975 in Basel's Barfusser Church, where historically wealthy people were buried.
She was laid to rest in the Basel church - but she was not fated to rest long: Based on archival discoveries, the team believes now that she was first found in 1843.
DNA samples from the mummy were compared with living descendants of the family to reveal the conclusive result.
But nobody knew who she was for a number of years, until late last year newly discovered archives led researchers to believe the mummy was a member of a well-established Basel family, the Bischoffs.
Now the scientists and the historians were sure: the mummy was none other than Anna Catharina Bischoff.
The mercury preserved her body - allowing researchers to identify her today.
Genealogists were able to trace Anna Catharina's descendants through birth, marriage, and death records.
Anna Catharina was born in Basel in 1719 and spent most of her adult life in the French city of Strasbourg.
She is likely to have contracted syphilis while caring for patients affected by the sexually transmitted disease.
It's thought Anna Catharina had seven children, of which only two survived childhood.
But before her death in 1787, she returned to Basel for syphilis treatment.
Their daughter Yvonne married Osman Wilfred Johnson Kemal and their son, Stanley Johnson, went on to have British Foreign Secretary Boris Johnson.