A doctor accused of murdering his Brisbane socialite fiancee after discovering she was in contact with an ex-lover faces a second trial over her death.
Dr Thomas Chris Lang, now 68, pleaded not guilty to murdering Maureen Boyce on the opening day of his retrial in the Brisbane Supreme Court on Monday.
The retired US doctor claimed to have been asleep in another room before he found the former fashion model's body in her Kangaroo Point penthouse on the morning of October 22, 2015.
Crown prosecutor Todd Fuller said Ms Boyce's bloodied body was found in bed, covered with a pillow and a blanket.
"She was found with a kitchen knife embedded in her abdomen down to the hilt," Mr Fuller said in his opening address.
"The tip of which had penetrated through to her back, on the opposite side into the sheet on the bed below her."
Ms Boyce was stabbed five times with such force that the blood-stained bedding was pierced three times by the 19cm blade.
Forensic officers also found a single drop of blood on the carpet beside the bed, which matched the victim's DNA.
Mr Fuller said the accused was the only other person in the apartment on the night she died.
The court heard Ms Boyce and Lang had known each other for more than 30 years and had an extramarital affair in the United States in the 1970s.
When Ms Boyce returned to Australia, she was pregnant with Lang's son who she raised with her husband Graham.
Mr Fuller said Ms Boyce told Lang about his son in 2013 and the pair had rekindled their relationship in the years leading up to her death.
Despite her still being married, Lang claimed the pair were engaged and intended to wed before Christmas.
The couple had gone to dinner the night of the murder and had been drinking when they argued over text messages.
Lang told police Ms Boyce had gone through his emails and claimed she would "hook up" with an ex-boyfriend before she had thrown her mobile phone from the balcony during an argument around 9pm.
A forensic examination later revealed text messages from one of her former lovers had been accessed just before midnight and a call placed at 12.04am.
Lang told police it was like a "stab to the heart" to discover she was still in contact with her former lover.
However, Lang told police Ms Boyce went to bed alone after the argument at about 9.30pm, asking him to sleep in another room.
He went to bed around 11.30pm and claimed to have found Ms Boyce dead the next morning.
Lang told police Ms Boyce had been depressed in the days before her death and the Crown conceded she had struggled with mental illness all her life.
Defence barrister Ruth O'Gorman said the evidence would show the wounds could have been self-inflicted and police did not find Lang's DNA on the weapon.
"It's a complex story because it involves complex emotions, but in reality, it comes down to one simple question - did this man kill Maureen Boyce, or did she take her own life?" Mr Fuller said.
The trial before Justice Ann Lyons continues.