A mother and son involved in a stabbing were both acquitted of assault-related charges early this morning.

Douglas Allen, 19, was charged with assault with a weapon and aggravated assault for stabbing his mother's ex-boyfriend, Allan Bullers, in October 2008.

Yukon Supreme Court Justice Leigh Gower found him not guilty on both counts.

Douglas' mother, Heather Allen, 39, was also found not guilty of her charges of general assault and aiding and abetting an assault.

Douglas was acting in self-defence when he plunged a knife into the back of Bullers, Gower ruled this morning.

On the day of the incident, Douglas arrived home at about 1:30 a.m. to find Bullers' car outside his Riverdale townhouse.

Bullers and Heather had a romantic history, but had broken up after Bullers crashed his truck while Heather was a passenger. She suffered a fractured wrist, femur and ribs as a result of the incident.

While they were together, Douglas was witness to many occasions on which Bullers verbally abused his mother. He was also privy to an incidence when Bullers physically assaulted Heather, causing her to have a black eye and cuts on the inside of her mouth.

In court last week, Douglas testified that he was "terrified” of Bullers and what he could do.

Unbeknownst to Douglas, on Oct. 18, 2008, Bullers and Heather had been seeing each other in secret.

When Douglas recognized Bullers' car, he called his mother and asked her if Bullers was in the house with her. Even though Bullers was in the bedroom with her, she denied he was there, and the phone call ended.

After the call, Bullers asked Heather who had been on the other end of the line. Was it Douglas?

When Heather denied it was Douglas, Bullers attempted to grab the phone from her. He took hold of her fractured wrist, which was still healing.

As she attempted to push him off her using her hands and knees, she fell off the bed, which left her in considerable pain.

She yelled at Bullers to "Get the f--- out of my house!”

Meanwhile, Douglas had arrived and was downstairs when he heard Heather yelling or screaming.

In court last week, he testified that when he heard his mother's voice, "My skin crawls, my hair stands up and my adrenaline starts pumping.”

He believed his mother was in trouble.

He grabbed a kitchen knife, which he thought he would use as an intimidation factor against his mother's aggressor.

With his steel-toed boots still on, he stomped up the stairs.

As he reached his mother's bedroom, she opened the door and told her son to get Bullers out of the house.

Douglas walked over to Bullers, who was sitting on the bed, and kicked him in the chest.

Bullers then stood up and said, "Do you want to go, Doug?”

Douglas hesitated for a moment while he contemplated putting the knife on the dresser. Before he had a chance to respond to Bullers' question, Bullers punched him and knocked him on the bed.

Gower said he believed Douglas' evidence that he did not hit Bullers while Bullers was on top of him and punching him in the face.

Douglas told the court last week that soon after Bullers started punching him, Douglas told him, "Get the f---- off me! I've got a knife! I will stab you!”

When Bullers didn't comply with his request, Douglas stabbed him in the back, making sure to avoid his heart.

Gower also believed this to be true, he told the court this morning.

Bullers then fell on Douglas, and the teenager tried to get out from beneath him. During that struggle, he kneed Bullers in the head, leaving him with a bruise that was documented by Whitehorse RCMP and filed as an exhibit for the trial.

Gower said this morning that "there is an air of reality” in Douglas' defence of self-defence.

Given Bullers' age, life experience, height and weight, Gower determined Douglas believed he had to stab Bullers to prevent grievous bodily harm.

However, Gower did determine that it was not "necessary” for Douglas to give Bullers the initial kick in the chest.

In his testimony, Bullers alleged that Heather had hit him in the head before Douglas entered the room. He also claimed she had hit him on the back while he was on top of Douglas.

In acquitting Heather, Gower said he believed her evidence that throughout the struggle between Douglas and Bullers, Heather stood off to the side, watching.

She also said that she had not hit Bullers in the head before Douglas entered the room.

Gower determined her evidence to be true because Bullers' testimony "simply defies common sense.”

At the time of the incident, Heather was still recovering from the traffic mishap that had left her with many fractures.

Someone in her "frail” condition would not have hit Bullers with the kind of force it took to leave the large, dark bruise on the side of his head, the judge ruled.

There were other aspects of Bullers' testimony Gower found unbelievable.

The judge said Bullers was "unconvincingly absolute” about some of the evidence in his testimony, but made contrary statements during cross-examination.

Gower said the tone of Bullers' evidence was that he had no particular issue with Douglas, but Douglas testified he was "terrified” of Bullers.

After Douglas stabbed Bullers, he told Bullers he hated him and he had ruined his life.

Gower said he would expect Bullers to at least be aware of Douglas' animosity toward him and make some reference to it in the testimony.

Gower also made reference to a time during Bullers' testimony when he described the moments after he was stabbed.

Bullers was "quite emphatic” that as he went down the stairs, he saw Heather smiling with blood on her shirt and the knife in her hand.

"It seems to me this was an attempt by Mr. Bullers to portray Ms. Allen in a cruel and calculating light,” said Gower.

When Gower handed down his ruling, Douglas hugged his defence lawyer, Andre Roothman, while Bullers quickly left the courtroom.

A wealth of family and friends of the Allens attended the reading of the verdict.