Denville Hall, a northwest London care home for elderly actors, said Byrne died on Tuesday.
Her death came eight days after that of Mayall, who died aged 56 from a sudden heart failure following a run.
Byrne played Nursie — Queen Elizabeth I’s bonkers former nanny, whose real name was Bernard — in “Blackadder II”.
She and Mayall shared a memorable scene during the 1986 second series, which was set in the Tudor era.
Following a grand entrance, Mayall’s sex-obsessed lothario Lord Flashheart barks at Byrne’s plump, middle-aged character: “Nursie! I like it firm and fruity!”
Educated in Kent, southeast England, Byrne joined the Royal Shakespeare Company, and played parts on the London stage.
“Blackadder” was voted Britain’s second-best situation comedy series in a 2004 BBC-organised poll won by “Only Fools and Horses”.