A man accused of killing his 65-year-old housemate by setting him alight had claimed to be the Queen's grandson, a court has been told.
David Charles "Yankee" Edgerley, 39, has pleaded not guilty to murder at a Brisbane Supreme Court trial after Victor Graveson died in September 2017.
Edgerley allegedly doused Mr Graveson in petrol and set him alight as the 65-year-old slept at his Alexandra Hills home before holding a door closed to ensure there was no escape.
A friend saw Mr Graveson screaming in pain inside the house as he tried to flee the flames while Edgerley held the door, crown prosecutor Caroline Marco said.
Edgerley released the door and fled after he was struck with an object by the friend, the court heard.
"Mr Graveson emerged from his house on fire. The hair on his head and beard was scorched," Ms Marco told the jury.
"His clothing was either burning or burnt off. His skin was peeling off him and the soles of his feet were bleeding."
Mr Graveson was hosed down by relatives before telling them Edgerley had "lit him up".
He was taken to hospital in a critical condition with burns to 80 per cent of his body but died three days later.
Edgerley committed the "unspeakable act of violence" while high on meth for three days straight, the crown prosecutor said.
"The effect of the drug ... caused him to believe irrational thoughts including that the deceased had raped his niece who lived in America," Ms Marco said.
Edgerley's behaviour had been "peculiar" at the time, telling people he was a member of the British royal family and "had to go to England because the Queen was going to give him a crown", the court heard.
Edgerley earned his nickname because he was born in the United States, had an American accent and frequently wore a New York Yankees hat.
The trial before Justice Soraya Ryan continues.
