The British entertainer who died on Saturday, aged 72 was ailing and told a childhood friend that her late husband Bobby was "waiting for me".
Black admitted to Terry McCann, whom she had known for years that she was going to die.
"I wasn't surprised when I found out she had died," he told BBC News.
"The last thing she said to me was she was going blind, she showed me her hands, she had arthritis," he said. "She willed herself to die. She said, 'Bobby's waiting for me.'
"Her mother went the same way. I don't know what her mother died of but it seemed she associated it with her mother's death and she just knew it was going to happen.
"She just said, 'Look at me, I'm a wreck.' I was trying to cheer her up. She knew something we didn't.
"She knew she was going to die and she said she wasn't going to linger like her mother.
"Her mother was ill for two years and she had the same complaint and she said she was never going to linger like that."
A post-mortem has been carried out although the results are not expected to be officially published for days or even weeks. However, Spanish police say it's probable that Black died of natural causes.
An official told The Guardian there was nothing to suggest the death had been suspicious – but it could have been as a result of an accident.
"There were no objects that had been disturbed in her home, there were no signs of violence on her body,"she said.
"This needs to be confirmed by the postmortem, but the evidence gathered by the police suggests that she died of natural causes, but that her death might have been provoked by an accident.
"At this stage, we can't know if she banged into something and this provoked her death – these are just theories at this point."
The Liverpudlian was found on her balcony by her son, according to BBC News correspondent Robert Hall. Paramedics arrived on the scene at 18.00 local time (17.00 BST) but were unable to resuscitate her.
A book of condolence for the singer was opened at Liverpool Town Hall, where the flag is flying at half mast, and so far around 400 – 500 people have left messages. The book will be open until Friday.