Downton Abbey star Nathalie Baye is dead after a battle with dementia. She was 77. Baye died in her home in Paris after receiving a Lewy body dementia diagnosis, the actress' family confirmed to the Agence France-Presse on Saturday, April 18. 'Downton Abbey' Stars: Where Are They Now? According to the Mayo Clinic, Lewy body dementia, also known as LBD, occurs when protein deposits called Lewy bodies develop in nerve cells in the brain and affect brain regions involved in thinking, memory and movement. This story is developing.