Cilla's son found her body on a terrace after breaking door down
Cilla Black's son Bobby discovered the star's body after smashing his way into her bedroom when she failed to rise from a siesta.
The legendary singer and TV presenter's eldest child broke open her door after he had gone to see if she was alright late on Saturday afternoon and received no response.
Spanish sources said Cilla's son found her lying on her back on a sun terrace adjoining her bedroom.
She was already dead by the time he found her in her villa near the Costa del Sol resort of Marbella.
Paramedics arrived at the property in a quiet cul-de-sac around 6pm on Saturday but could do nothing to save her.
Cilla's body was removed around 1.30am on Sunday after police, a forensic expert and the judge in charge of a routine investigation into Cilla's death had visited the scene.
Traffic jams in the area, caused by a nearby David Guetta concert, are understood to have delayed the arrival of some of the officials who were called to the detached property - called Casa Roll - and led to the agonising wait before the body was taken away.
It was driven directly to the Forensic Medicine Institute in Malaga, where a post-mortem is expected to take place.
Spanish police confirmed on Sunday that they were awaiting autopsy results but said everything was pointing towards Cilla's death being the result of natural causes.
However, sources close to the investigation said medical examiners would look closely at marks on her right arm and elbow, which they believe may be linked to a fall possibly caused by a sudden temperature change.
A source close to the inquiry said: "Cilla's son found her lying face upwards in a solarium-style sun terrace next to her bedroom.
"There's no conclusive autopsy results yet, but the main theory right now is that she had a dizzy turn after going from an air-conditioned room into the midday heat and losing her balance.
"The marks she's got are consistent with a fall where she has put up an arm as a defence mechanism.
"What needs to be determined now is why she fell and whether it was indeed to do with the sudden change in temperature and the effect that had on her - which seems the most likely scenario at the moment - or whether something else triggered the collapse.
"Midday temperatures on Saturday in the area were in the high eighties (30C-plus) and we know Cilla wasn't in the best of health. More tests may be necessary after the autopsy to get to the bottom of what's really happened.
"There is no evidence to link Cilla's death to any criminal act but police and courts generally like to keep an open mind on things."
The possibility that the singer and TV star fell because she was confronted on the terrace by a would-be burglar has also been looked at and has not yet been excluded, although it is not really being seen as a probable scenario.
Investigators believe Cilla died at some point between 1.30pm on Saturday - when she went upstairs for her afternoon nap - and 3.30pm.
Her eldest son is understood to have jetted to Spain the day before the tragedy.
Spanish authorities have not confirmed whether Cilla, who suffered crippling arthritis and hearing problems, arrived before or with Bobby.
He is now staying at a different property in the area.
His younger siblings Ben (41) and Jack (34) are staying at the house where their mother died after flying to Spain when they heard the news of her death.
Cilla, who was born Priscilla Maria Veronica White in 1943 in Liverpool, told last year how she would like to die at around the age of 75 before she became too frail to enjoy life.
She said: "Seventy-five is a good age to go. I know it's only four years away but I take each day as I find it."
Speaking of how she watched her mother Priscilla endure a slow and painful death from the bone disease osteoporosis in 1996, she said: "It wasn't a good experience. My biggest fear is going like that when I can't control my body."
A fan today laid flowers outside Cilla's home.
The message on the bouquet said: "RIP Cilla Black. With love from all your British fans in Spain."