Man jailed for murdering MMA fighter in fit of 'sexual jealousy'

A man has been given a life sentence for murdering a "beloved" MMA fighter in a fit of "sexual jealousy".

Kai Pennell, 35, was told he would serve at least 22 years in jail for stabbing Duane Keen, 47, at a flat in Blaenavon, south Wales, where a woman they had both previously been romantically involved with, Rebecca Phillips, was living.

In an emotional court statement, Duane Keen's son, Joshua Keen, told Pennell he was a "coward" who had shown "no remorse".

Sentencing Pennell, Justice Stacey said the case was "heartbreaking", remarking on Duane Keen's "outstanding qualities and commitment to his family".

Phillips had split with Keen in May 2025, before starting a relationship with Pennell which ended in September 2025.

Pennell, of Blaenavon, remained "obsessed" with Phillips after they separated and grew increasingly jealous of Keen, Cardiff Crown Court heard on Tuesday.

The court heard about messages and phone calls between Pennell and Phillips in the days before the murder which prosecutor Christopher Rees KC described as "demanding and controlling".

He said they showed Pennell was "obsessed with [Phillips] and burning with jealousy".

"You make my heart melt and my blood boil at the same time," Pennell wrote in one message.

Another read, "What have you done to my heart, I want it back."

On 17 October, 2025, the night of the murder, Pennell had bombarded Phillips with "disturbing" calls and text messages, accusing her of seeing other men.

Feeling unsafe, she asked Keen to come to her address, where they were both ambushed by Pennell.

CCTV footage showed Pennell outside the flats, peering through the spy hole in the front door, before selecting a large kitchen knife, around 8 to 9 inches long.

The prosecution said this was the point where Pennell made "a decision to kill".

Phillips told investigators she and Keen were in bed when they heard someone fiddling with the lock and "booting the chain off the door".

She said Pennell "pounced" on Keen and both men began "grappling".

Phillips said she ran to fetch a neighbour, and when she returned there was "blood all over the walls".

"Kai was like a demon had taken over his body," she said. "His face was petrifying."

Pennell then fled the scene before being found by police helicopters in a wooded area close to the flats a few hours later.

A post-mortem examination recorded a number of stab wounds to Keen's body, as well as slash wounds on his arms where he had tried to protect himself.

When interviewed by police, Pennell answered "no comment".

Toxicology reports found no alcohol in his system but levels of heroin, cocaine and methadone were detected, likely to have been from use over the previous 24 hours.

However, the court heard it was "not possible" to know what impact the drugs may have had on Pennell, who was a long-term drug user.

The court heard Duane Keen was "well known in the mixed martial arts community" as a fighter and as a coach of young people.

Duane Keen's son, Joshua Keen, read a victim impact statement to the court, looking at Pennell and shaking his head as he sat down.

He called Pennell a "cowardly man", who had shown no remorse, accusing him of "smirking" in the dock.

He said Pennell should "not be let out of prison for the rest of his life".

Joshua went on to describe his father as being "best mates" with his sons, and a caring grandfather.

"[He was] our protector - there was nothing he wouldn't do for us," he said.

Defending, David Elias KC said only a life sentence was possible, but Pennell's guilty plea meant the family and witnesses had been spared the ordeal of a trial.

He said Pennell had been diagnosed with ADHD at about the age of ten, and had suffered mental health problems, including being sectioned in 2023.

The court heard Pennell had previous convictions, but no details were given to the court - although the judge referred to them as "minor."

Sentencing Pennell to a life sentence, with a minimum term of 22 years and 238 days in jail, Justice Stacey said his behaviour had been "volatile" on the day of the attack, noting he was "spiralling out of control".

She said: "In your twisted and self-piteous logic, you told her [Phillips] that your murder of Duane was somehow her fault.

"The only person to blame for Duane's murder is you.

"You were motivated by sexual jealousy and anger when you killed Duane, and as a way to try and control and punish Rebecca for breaking up with you and remaining friends with Duane."

She said other charges relating to threats to kill Phillips would remain on file, and imposed an indefinite restraining order prohibiting Pennell from contacting his ex-partner.