Herbert Huscher’s work in the 50s and early 60s uncovered evidence of the identity of Charles Clairmont’s putative father, Charles (Karl) Abram Marc Gaulis. Charles died in 1796 in Schmiedeberg, Silesia, not in 1798 as claimed by Mary Jane, so he could not have been Claire’s father. We do not know whether Claire, throughout her life, continued to believe that he was.
As far as we know, both Mary Jane and Charles Gaulis traveled to Bristol from Cadiz in around 1794. Huscher (1957) cites the transcript of a letter of Mary Jane’s, written in 1830 and now in the possession of Dr. Walter Clairmont (grandson of Charles): this letter indicates that Charles ‘Clairmont’ the elder originally came from Lausanne and met Mary Jane in Cadiz where she was staying with her brother. The inference from the same letter is that they both returned to Bristol where Mary Jane made the acquaintance of Lady Clinton, Charles Gaulis’ sister. Huscher (1960) further cites a letter from Juste Gaulis to Charles in 1794 (received by Charles 8 August): at that time Charles was staying with the merchant firm David Duveluz & Co, in 14 Sise Lane, Budge Row, London. Charles was also associated with the Swiss firm of Pierre Durand and Christin in Cadiz.
Charles and Albertina Marianna Gaulis were the children of Jean Abram Roldolphe Gaulis, a landowner and magistrate of Lausanne, Vaud, Switzerland. The eldest child, Abram Frederic Louis Juste Gaulis, was the heir and chatelain of the chateau of Colombier-sur-Morges, near Lausanne, and member of the Grand Council of Vaud. His wife Jeanne Marie Bergier was a daughter of Elie, Lord of Vuarrens. Albertina Marianna Gaulis married Robert George William Trefusis, 17th Baron Clinton in April 1786. She died in February 1798, a year after her husband.  The heir Robert Cotton St. John Trefusis was only 11 years old when his mother died.
Charles Rodolph Trefusis, 19th Baron Clinton,son of Albertina Marianna Gaulis
Biographers have speculated on the origin of the name 'Clairmont' adopted by Mary Jane Vial. No evidence has been discovered to support her claim that Charles Gaulis adopted Clairmont as an anglicised surname. It seems more likely that 'Clairmont' is merely one of a number of aliases Mary Jane adopted to conceal her true status and identity. For instance, while in London, Bristol and Wales in 1797 she was known as Mrs St. Julian: it was under this identity that she was arrested for debt and imprisoned in 1799. However, it is worth noting that Charles Gaulis' brother Juste was Chatelain of Colombier-sur-Morges and Cottens, in the Morges district of the canton of Vaud: the tiny village of Clarmont is within a couple of kilometres of both.
We do not know whether Charles Gaulis’ presence in Schmiedeberg (where he died) represented the end of his liaison with Mary Jane, or whether this was a normal business trip: nor do we know most of what happened to Mary Jane between Charles’ death and the birth of her daughter in 1798.