She was buried right in front of the altar, clearly well fed and was wearing good quality clothes, indicating she was just as wealthy as her distant grandson was destined to be.
Highly toxic mercury was used as a treatment for syphilis but was more often a kill than a cure and scientists say it was this that preserved her body.
Since 1975, when her mummified body was unearthed in a church in the Swiss city of Basel, she had been a scientific mystery - a well-preserved corpse buried with proofs of her wealth, who for lack of identification took on a distinguished title: the Lady from Barfüsser church.
The corpse of the woman - who'd lain unidentified for years - was discovered in Basel, Switzerland.
Unfortunately the treatment did not work and scientists believe she died from mercury poisoning in 1787 at the age of 68.
Genetic material extracted from the big toe of the mummy was compared to DNA donated by modern members of the Bischoff family.
Those records led historians to suspect she was a member of the well-heeled Bischoff clan.
The results from the DNA showed that there was a 99.8% probability that the Johnson's descended from the mummy.
Researchers then set out to discover the genealogical tree of the woman.
Once her identity had been established, genealogists were able - with the help of the efficient records of births, marriages, and deaths which tend to be kept by the wealthier classes - to trace more of Anna Catharina's descendants.
It's believed Anna Catharina married a church minister and lived for most of her adult life in Strasbourg, the BBC reports.
She had contracted syphilis, probably from treating sufferers of the disease.
She had seven children.
Five generations later, Marie Luise von Pfeffel married Stanley Fred Williams; and their daughter Yvonne married Osman Wilfred Johnson Kemal.
"This discovery means that Boris Johnson is not only distantly related, albeit very far removed, to the present Royal Family but also to all the royal houses of Europe, including the Swedish and Dutch royal families, as well as the Romanoffs", the BBC said at the time.