Oscar Pistorius made a clandestine phone call to an old girlfriend nicknamed "Babyshoes" shortly before he killed Reeva Steenkamp, it has been claimed.

The athlete spoke for nine minutes with a young woman named Jenna Edkins on his phone as he returned home to his luxury mansion on the night he shot dead his girlfriend, according to reports.

Edkins was an former flame of Pistorius and their relationship pre-dated his fling with Samantha Taylor - whom he was dating four months prior to that fateful Valentine's Day, last year. The couple are said to have split when Edkins discovered his relationship with Taylor.

Journalists Mandy Wiener and Barry Bateman uncovered the record of the call, which was not mentioned during Pistorius' trial by either the prosecution or the defence.

Police never discovered that the call was made, said reports.

Wiener and Bateman are due to publish details about the call in an upcoming book on the Pistorius case.

They said one potential reason why the call escaped police attention was that the number was registered in the name of Edkins' father, meaning detectives made no connection between it and Pistorius' former lover.

Edkins is a new name in the Pistorius saga. She never made a statement, nor appeared in court. But she did defend the fallen track idol on social media in the wake of Steenkamp's slaying.

And she was once mentioned by Taylor's mother during an interview, who said: "Sammy once saw a Facebook profile picture of a woman called Jenna Edkins sitting on Oscar's bed with Kola, the puppy that Sammy and Oscar had bought together.

"He always denied he was having any contact with Jenna, but the picture proved otherwise."

Pistorius was convicted of culpable homicide last month and is awaiting sentencing later this month.