A man accused of stabbing his mother's ex-boyfriend was "terrified” of the victim in the years leading up to the incident, Yukon Supreme Court Justice Leigh Gower heard Friday.

Douglas Allen, now 19, is charged with aggravated assault and assault with a weapon after Allan Bullers, 38, his mother's ex-boyfriend, was stabbed on Oct. 18, 2008.

Douglas' mother, Heather Allen, 39, was charged with assault and aiding and abetting an assault in connection with the incident.

Both have pleaded not guilty to the charges.

On the night of the incident, Douglas walked in on Heather and Bullers having an argument at about 1:30 in the morning.

Moments earlier, Douglas had called his mom to ask her if it was Bullers' car he saw parked outside the residence. She denied Bullers was with her in the house, Douglas testified.

Shortly after their conversation, Douglas heard his mother screaming upstairs.

"The scream reminded me of excruciating pain,” he said.

"My skin crawls, my hair stands up and my adrenaline starts pumping.”

Douglas testified he got into a "fight or flight” mode and grabbed a kitchen knife.

As he held the knife, he thought he would use it as an intimidation factor. He stomped loudly up the stairs with his steel-toed boots still on to add to that factor, he said.

When he entered the room, he kicked Bullers, who was sitting on the bed, and shortly after, Bullers was on top of him, punching him, Douglas testified.

"He was on top of me and continuously hitting and hitting and hitting,” he testified.

Douglas shouted for Bullers to get off him and said he had a knife, but Bullers persisted and Douglas stabbed him, he said.

Douglas told the court of his history with Bullers throughout the five years he was dating Heather.

Douglas said he had witnessed Bullers being verbally abusive to his mother on many occasions, and Bullers would often call Heather a "bitch” and "c--t” when arguing with her.

"He would use words along those lines to belittle my mother and her being a woman,” Douglas said.

"I started to realize that this guy was no good for my mother.”

Despite the arguments, Bullers and the Allen family all moved into a new house in Granger together.

That was when Bullers started to "show his true colours,” said Douglas, adding that Bullers would throw "hissy fits” and abuse his mother physically as well as verbally.

"I felt uncomfortable living there under the same roof,” he said.

Bullers lived in the Granger house for only a few weeks before Heather asked him to move out.

"He wasn't too impressed and he ended up throwing another one of his fits,” Douglas told the court, adding that Bullers punched holes in the walls and ripped the railing down.

After Bullers had moved out, he managed to get into the house, even though the Allens had locked all the doors specifically to keep him out, said Douglas.

Bullers continued to enter their residence without permission, the court was told.

After the Allens had moved to Riverdale, Douglas testified, at one point, Bullers gained entrance into the house through a bedroom window.

On one occasion, Douglas and his friends had skipped class while Heather was out of town. The students had gone over to Douglas' house to grab some breakfast, he said.

About five minutes after they arrived, Bullers walked through the front door and yelled at Douglas and his friends for missing school, he said.

Douglas said he felt he understood what Bullers was capable of after witnessing his behaviour in the Granger house.

He was unaware if Bullers and Heather were seeing each other at the time, and he didn't know why Bullers would be in their house.

"At the time, I was scared. I was terrified of what he was going to do next,” he said.

Douglas and his friends then left the residence. They were walking down Lewes Boulevard when Bullers drove by on his motorcycle, stopped and threatened to physically harm them, Douglas told the court.

Another incident in the fall of 2008 reinforced Douglas' negative impression of Bullers, he added.

Douglas testified that Bullers threatened him a few days before the stabbing.

Douglas and his friends were in the living room of the Riverdale home when Bullers and Heather came downstairs.

As they walked by Douglas, Bullers allegedly gave him a look.

"It was, like, a face of hatred toward me,” he said.

Douglas said Bullers snapped his fingers, pointed at Douglas and said, "I cannot wait until the next time I see you, Doug.”

A verdict in the case is expected Friday.