A woman believed to be in her 60s was killed in the blaze at a house in Spottiswoode Gardens, Mid Calder, West Lothian.
She was reportedly named today as Helen Lauchlan.
Firefighters were called to the scene at around 11pm on Saturday night, with crews from Bathgate and Livingston battling the fire.
The fire was contained in the living room of the property, Lothian and Borders Fire Service said.
Investigations are still continuing in order to establish the cause, but reports today suggested it could have been caused by a discarded cigarette.
A neighbour said: “Everyone is in complete shock. Helen was a lovely lady.”