A new baptismal record has been found for Peter III and his first wife Anna Maria. Initially I only had two records available, one for their daughter Maria Elisabetha and one for Magdalena, but I have now found one in the same church records for a Susanna Mebreuer, baptized on February 15, 1759, with the parents listed as Petri (Latin version of Peter) Mebreuer and Anna Maria, and the church location in Geisenheim, Hessen-Nassau, Prussia. This age puts her in between her two sisters. I had previously pointed out that there were six years in age between them, noting it as peculiar for that time in history. So now, the mystery has been solved. I have updated the main article for Peter III with this new information.