Petra Pazsitka was last seen on 26th July 1984, heading to a dentist appointment.
From the dentist, she was supposed to get on a bus and go to her parents' house - but she never arrived.
Understandably concerned, her family phoned the police and launched a wide scale manhunt - and, a year later, police arrested a man identified to reporters only as Gunter K.
Police said the 19-year-old confessed to killing a 14-year-old girl in the same area as a bus stop that Petra would have used.
He later also confessed to Petra's murder and, in 1989, officials declared her legally dead.
So imagine their surprise when, two weeks ago, she was found alive and well and living in Düsseldorf, Germany.
The missing student, now 55, was found living under a false name by police who were investigating a burglary in the local area.
According to the International Business Times, Petra soon told officers that the name on the house door was not hers and she was the student from Braunschweig that had gone missing 31 years ago.
She used an out-of-date identity card to prove that she was the missing girl.
When pressed by officers for more details, Petra confessed that she had moved into an apartment she had been secretly renting and that she had saved DEM4,000 (€20,000) to create a new life for herself.
She spent the years living without any legal documentation, earning money by working illicit cash-in-hand jobs.
A spokesperson for Braunschweig and Wolfsburg Police said: "As to the motive of her disappearance, she gave no explanation and expressly said that she continues to want no contact with the public or her family."
Petra has, so far, refused to speak with the media or her family.
It remains to be seen as to whether or not she will ever reveal why she decided to go off the grid.