A member of Adolf Hitler's own family was one of those killed in the Nazi campaign to wipe out the mentally ill, according to two historians.
'Aloisia V' came from a family with a history of mental illness
The woman, named as "Aloisia V", was the great grandchild of Hitler's great aunt - his second cousin, once removed.
She was gassed to death on 6 December 1940, at a mental institution in Austria, historian Timothy Ryback said.
Medical files show she suffered from schizophrenia, depression, delusions and other mental problems, he said.
Aged 49 when she died, she was one of thousands of mentally ill people - considered sub-human by the Nazis - killed or sterilised in a euthanasia programme meant to eliminate them.
But Mr Ryback, a US historian who heads Germany's Obersalzberg Institute, said he and colleague Florian Beierl had come across several "cases of either physical or mental disabilities" in Hitler's own family.
It is unclear whether Hitler knew about Aloisia's condition, and her fate, the researchers said.
But the Gestapo had labelled Aloisia's line of the family "idiotic progeny" in a secret 1944 report.
Close to Hitler
Aloisia was the great-grandchild of the sister of Hitler's paternal grandmother, meaning she was part of the Schicklgruber side of the family, Mr Beierl said.
He said the Schicklgrubers were close to Hitler's family - and that Hitler's father helped get Aloisia's father a job as a civil servant in Vienna.
Mr Beierl said many of the Schicklgruber family "crashed into suicide and mental illness", until eventually "the entire line died out".
The historians say they have no conclusions on whether mental illness affected Hitler himself, but said they would hand their findings to an expert on hereditary diseases to see what his assessments were.