The foster brother accused of incest with slain Queensland schoolgirl Tiahleigh Palmer raised fears he may have gotten the 12-year-old pregnant, his bail application has heard.

Key points: Foster brother Trent Thorburn refused bail on incest, perjury charges

Foster brother Trent Thorburn refused bail on incest, perjury charges Statement from schoolgirl's friend alleged he had sex with Tiahleigh when carers went out

Statement from schoolgirl's friend alleged he had sex with Tiahleigh when carers went out Court told Trent abused his position as a big brother

Trent Thorburn, 19, was denied bail after being charged last night with incest, perjury and attempting to pervert the course of justice.

His father Rick Thorburn has been charged with murdering Tiahleigh, who had been in the family's care for months.

Rick Thorburn had been due to appear in court on Wednesday, but is in an induced coma after collapsing at Beenleigh police watch house, south of Brisbane, on Tuesday.

Tiahleigh's body was found on the banks of the Pimpama River last November, a week after she was last seen alive.

Flanked by security and wearing prison browns, Trent Thorburn sat quietly in the court that was packed with Tiahleigh's supporters.

In opposing bail, police prosecutor Sergeant Ellen French argued Trent Thorburn would be an unacceptable risk of reoffending given the way he had misled police during the investigation.

Sergeant French told the court he abused his position as a big brother and took advantage of Tiahleigh by having sex with her.

"The victim was put into the care and protection of this defendant and his family," she said.

"Rather than providing her with the care and the love that she required as a child, this defendant betrayed her trust, he abused his position of big brother and took advantage of her and the consequences are, her young life has been taken."

A statement had also been obtained from a friend of Tiahleigh, who said the schoolgirl had disclosed "that when her foster carer went out, their son would then have sex with her".

The statement said Tiahleigh told her friend as early as September 15 last year that "Trent tried to touch me", and that she had reported the behaviour to her foster mother.

Trent Thorburn has been charged with incest, perjury and attempting to pervert the course of justice. ( AAP )

The court heard Trent Thorburn was concerned he might have impregnated Tiahleigh and raised those concerns with a cousin.

It was also told his mother Julene Thorburn may have been aware of their relationship.

The court also heard that police had seen a social media conversation between Trent Thorburn and a cousin that revealed "he had sex" with his 12-year-old foster sister and had "only done so because she threatened to kill his dog".

Sergeant French then said that "none of that was disclosed" to police on the five separate occasions Trent Thorburn was asked about his involvement with Tiahleigh, during an eleven-month investigation into her death.

Rick Thorburn has been charged with Tiahleigh's murder. ( ABC News: Josh Bavas )

Trent Thorburn's lawyer John Ide argued his client would not be a risk if released on bail because of his lack of criminal history, and because he had not been charged as an accessory to murder.

But the magistrate ruled that at this point she felt he would present an unacceptable risk and she did not feel comfortable releasing him.

He was remanded in custody. His case is due back in court on November 9.

Rick Thorburn was charged on Tuesday with murdering the 12-year-old and dumping her body in a river, with the arrest coming 11 months after Tiahleigh's body was found.

At the time, it was reported that he had dropped Tiahleigh off at school the morning she disappeared.

Six days later fishermen found her naked body on the banks of the Pimpama River.