Life Sentence for Murder of MMA Fighter in Jealousy Case
A man has been sentenced to life imprisonment for the murder of a well-regarded mixed martial arts (MMA) fighter, an act driven by "sexual jealousy."
Kai Pennell, aged 35, was ordered to serve a minimum of 22 years in prison following his conviction for stabbing Duane Keen, 47, at a residence in Blaenavon, South Wales. The flat was occupied by Rebecca Phillips, a woman who had previously been romantically involved with both men.
During the sentencing hearing, Duane Keen's son, Joshua Keen, delivered an emotional statement condemning Pennell as a "coward" who exhibited "no remorse" for his actions.
Justice Stacey described the case as "heartbreaking," highlighting Duane Keen's "outstanding qualities and commitment to his family."
Phillips had ended her relationship with Keen in May 2025 before beginning a relationship with Pennell, which concluded in September 2025.
Despite their separation, Pennell remained "obsessed" with Phillips and became increasingly jealous of Keen, according to evidence presented at Cardiff Crown Court on Tuesday.
The court reviewed messages and phone calls exchanged between Pennell and Phillips in the days preceding the murder. Prosecutor Christopher Rees KC characterized these communications as "demanding and controlling," demonstrating Pennell's obsession and intense jealousy.
"You make my heart melt and my blood boil at the same time," Pennell wrote in one message.
Another message read, "What have you done to my heart, I want it back."
On the evening of 17 October 2025, the night of the murder, Pennell sent Phillips numerous "disturbing" calls and text messages, accusing her of seeing other men.
Feeling unsafe, Phillips requested Keen to come to her flat, where both were ambushed by Pennell.
CCTV footage captured Pennell outside the flats, looking through the spy hole in the front door before selecting a large kitchen knife approximately 8 to 9 inches in length.
The prosecution asserted this moment marked when Pennell made "a decision to kill."
Phillips informed investigators that she and Keen were in bed when they heard someone tampering with the lock and forcing the door chain off.
She described Pennell "pouncing" on Keen, leading to a physical struggle between the two men.
Phillips ran to fetch a neighbor, and upon returning, observed "blood all over the walls."
"Kai was like a demon had taken over his body," she said. "His face was petrifying."
Pennell fled the scene but was located a few hours later by police helicopters in a wooded area near the flats.
A post-mortem examination revealed multiple stab wounds on Keen's body, along with slash wounds on his arms, indicating defensive injuries.
When questioned by police, Pennell declined to comment.
Toxicology reports found no alcohol in his system but detected heroin, cocaine, and methadone, likely consumed within the previous 24 hours. The court noted it was "not possible" to determine the drugs' impact on Pennell, who had a history of long-term drug use.
Our Protector
Duane Keen was recognized within the mixed martial arts community both as a fighter and as a coach for young people.
Joshua Keen, Duane's son, read a victim impact statement to the court, shaking his head at Pennell, who appeared to smirk in the dock.
He labeled Pennell a "cowardly man" who showed no remorse and insisted that Pennell "should not be let out of prison for the rest of his life."
Joshua described his father as "best mates" with his sons and a devoted grandfather.
"[He was] our protector - there was nothing he wouldn't do for us," he said.
Restraining Order and Sentencing
Defence counsel David Elias KC acknowledged that only a life sentence was appropriate but noted that Pennell's guilty plea spared the family and witnesses the trauma of a trial.
He stated that Pennell had been diagnosed with ADHD around age ten and had experienced mental health issues, including being sectioned in 2023.
The court heard Pennell had prior convictions, described by the judge as "minor," though specific details were not disclosed.
Justice Stacey sentenced Pennell to life imprisonment with a minimum term of 22 years and 238 days, citing his "volatile" behaviour on the day of the attack and that he was "spiralling out of control."
"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."
Other charges related to threats to kill Phillips remain on file, and an indefinite restraining order was imposed, prohibiting Pennell from contacting his former partner.
