A teenager who was stabbed by his relative as he walked off a Fremantle bus has died in hospital.
The 18-year-old man died at the weekend after being allegedly stabbed in the chest by his relative, Tanya Ugle, on Wednesday.
A police spokesman on Thursday alleged the pair boarded a bus at Fremantle Train Station around 2.15pm, but the bus driver stopped the bus shortly after departing the station due to the conduct of the woman.
The 35-year-old woman was then asked to exit the bus.
"It will be alleged once out of the bus the woman produced a knife and assaulted the 18-year-old man, who is related to her," the police spokesman said.
"The 18-year-old man received an injury consistent with a stab wound to his chest and collapsed.
"The woman left the scene."
Since the teenager's death, major crime squad detectives have taken over the investigation.
Ms Ugle has been charged with grievous bodily harm but that charge may be upgraded during her next court appearance in Fremantle Magistrates Court on Friday.