A man who admitted to stabbing a carpenter over a bitter love triangle has had his murder conviction and 20-year jail term quashed.

But an appeal court today found the jury was wrong to convict Smith of murder because there was reasonable doubt he may have acted in self-defence.

Smith stabbed his love rival once in the chest at a home Pettersson had stormed into in the Newcastle suburb of Jesmond in January 2022.

His 20-year prison term also overturned, Smith now faces a District Court trial for the lesser charge of manslaughter.

Smith had a fluctuating relationship with a woman from 2016 until the day of the incident, whereas Pettersson was in a relationship with her from August to December 2019.

When Pettersson and the woman separated, he moved to Queensland.

The woman found out a few months later she was pregnant and told Smith he was the father before giving birth in July 2020.

In May 2021, Pettersson returned to Newcastle and moved into his recently purchased home when the woman reached out, suggesting he could be the father of her baby boy.

He decided to take a paternity test and during this time the woman would sometimes stay with him despite being in a relationship with Smith.

In August 2021, the DNA test proved Pettersson was the boy’s biological father and Smith found out he had been lied to about paternity.

Smith was with the woman on January 6, 2022, at the Jesmond house when an aggressive, upset Pettersson pulled up outside about 3.34pm.

Pettersson had called the woman 17 times and her father seven times as he wanted to see his son before deciding to drive to her home.

There was a confrontation in the kitchen between the two men and Pettersson was stabbed once in the chest.

Nonetheless, no witnesses from the house observed the deadly confrontation, which led the Court of Criminal Appeal to determine that there was reasonable doubt as to whether Smith acted in self-defense.

“There was a lengthy history of animosity between the applicant and the deceased, which included mutual threats,” the appeal judgment states.

Pettersson lunged at Smith after he put the knife away and Smith was not in a position to be able to escape the house, the appeal court found.

By attempting to take the knife off him, Smith would have been in “mortal danger” had Pettersson used it against him, Justice Christine Adamson said.

Smith will apply for bail when the case returns to the District Court on October 17, his solicitor Mark Ramsland told AAP.