Scientists in the Swiss city of Basel have finally identified a mysterious mummified body after more than 40 years – and discovered that the woman was a relative of the UK foreign secretary, Boris Johnson.

The corpse has been identified as Anna Catharina Bischoff, who died in 1787. Her body was first uncovered in 1975, while Basel’s Barfüsser church was being renovated. It was well preserved because of a high level of mercury in the remains, often a sign that a person had been treated for syphilis. The site of her burial, in front of the church’s altar, indicated that Bischoff was probably of high status.

An artist’s impression of how Anna Catharina Bischoff may have looked in life, prepared for the SRF TV show about the discovery. Photograph: SRF

A new study of the body extracted DNA from the mummy’s big toe, and this was compared with DNA from descendants of the Bischoff line. A 99.8% match was found, and the relationship to the Johnson family is confirmed by records of births, deaths and marriages.

Bischoff’s daughter married Christian Hubert Baron Pfeffel von Kriegelstein, and several generations of Von Pfeffels later, the family line reaches Boris Johnson’s father, Stanley.

Boris Johnson is yet to comment on his rediscovered great-great-great-great-great-great-great grandmother. Photograph: Kirsty Wigglesworth/AP

Swiss public television channel SRF 1 is airing an edition of science programme Einstein about the hunt for the mummy’s identity.

Boris Johnson is yet to comment on the rediscovery of one of his 512 great-great-great-great-great-great-great-grandparents.