Reality star Kylie Jenner. [Source: AP News]

LOS ANGELES (AP) — Kylie Jenner testified Monday that she expressed concerns to her brother Rob Kardashian about his new girlfriend and soon-to-be reality TV co-star Blac Chyna.

Since she had heard Chyna had a tendency to abuse drugs and alcohol and become violent.

“I felt it was my duty to express my concerns, but ultimately it was up to him,” Jenner, now 24 and a teenager at the time, said from the witness stand at a Los Angeles trial. She said her brother didn’t heed her warnings and continued with the relationship.

Chyna is suing Jenner and three other members of the Kardashian family, alleging they defamed her as violent and forced the cancellation of her reality show, “Rob & Chyna,” after one short season.

The 2016 show, a “Keeping Up With the Kardashians” spin-off, grew from the relationship of Chyna and the youngest of the Kardashian children.

Both Chyna and Jenner had previous relationships with the rapper Tyga, who Jenner said told her dark stories of his time with Chyna. Tyga showed her a 6-inch knife scar he said she gave him while abusing drugs and alcohol, Jenner said.

Jenner testified that she knew Chyna, who had befriended her sister Kim Kardashian and spent time around the family, but did not consider a friend before Rob Kardashian began dating her in January of 2016.

Rob Kardashian and Chyna would announce their engagement in April of that year, announce that Chyna was pregnant in May, launch their reality show in September and have a daughter, Dream, in November.

In December, the couple would have an all-night celebration of their show being approved for a second season that turned into a bitter fight.

That dispute, and how violent it may have become, was at the centre of testimony from both Chyna and from Jenner’s mother Kris Jenner. Chyna said she was being playful when she wrapped a phone-charging cord around her fiancé’s neck and grabbed his gun. Kris Jenner, who did not witness the fight, testified through tears that she felt that Chyna had tried to “murder” her son.

On Monday, when asked by Chyna’s lawyer Lynne Ciani if she felt anger toward Chyna, Kylie Jenner answered, “Probably, after I heard about the attack on my brother.”

The two other defendants, Khloé Kardashian and Kim Kardashian are expected to testify later in the week. Kim Kardashian was not in court Monday for the first time in the six-day-old trial.