Peaches Geldof made secret trips to a rehab clinic in the weeks before she died.
The 25-year-old presenter - whose death last month was "likely" due to heroin - was spotted at least six times at the facility in Maidstone, Kent, but her husband Thomas Cohen reportedly didn't know she was visiting the centre to collect prescriptions for methadone, a drug used to help addicts off heroin.
A source who met her at the clinic told The Sun newspaper: "We were on first name terms but I called her 'P'. I last saw her a couple of weeks ago. She was fine, but furtive.
"She used to wear a hoodie to disguise herself. The first time I saw her I thought I recognised her and we just chatted about a few things.
"I said, 'I recognise you from somewhere' and she told me her name was Peaches. That was when it clicked -- Peaches Geldof.
"She said, 'You'd better not say anything to anybody'. She didn't want her husband finding out.
"She said he was completely straight and that her dad would go spare if he knew anything about it.
"She seemed like a really normal girl. To me she was a celebrity."
According to the unnamed insider, Peaches - who had sons Astala, two, and Phaedra, 12 months - claimed her spouse wouldn't "understand" her problem and she worried about the impact it would have on her family life.
The source added: "She said she didn't want her family or her husband to know about the drugs and it was top secret. She used to arrive on her own. She was on a script [prescription] and had to turn up weekly.
"She was most concerned about her husband. She said, 'You won't believe it he's a really straight family man. I married a really straight really nice bloke. He won't understand, it would affect my kids'."
In 2008, Peaches was reported to have stopped breathing after a drugs overdose and had to be revived.
Two years later, an American blogger posted an account of an alleged one night stand with the British star and claimed they had taken heroin together.
Her publicist later denied the allegations.