Bethany Hill, 20, was found dead with neck injuries in Stratford-upon-Avon on 3 February last year.
It is alleged she was killed by Jack Williams, 21, and his girlfriend, Kayleigh Woods, 23, at the flat they all shared in Hertford Road.
The pair, who are on trial at Warwick Crown Court, deny murder.
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Opening the case, prosecutor Stephen Linehan QC said Miss Hill was a former girlfriend of Williams and had a "volatile" relationship with Woods, a transgender woman with whom she had planned to have a child.
Jurors heard Miss Hill was found dead by a police officer in a blood-drenched bathroom.
Mr Linehan QC told the court: "In the course of the killing, Beth's wrists were bound together with duct tape and the blade was used to inflict repeated cuts across the back of her neck before she was killed by the jugular vein being cut through."
He said Miss Hill was found dead after Woods, formerly known as Kyle Lockwood, dialled 999 at 19:07 GMT on 3 February, telling the operator: "Well my best friend is dead in my flat."
Alleging the "sadistic" killing may have been carried out for "perverted pleasure", Mr Linehan QC said: "What she was saying was that her friend had killed herself while she was out of the flat and that she had returned to find blood everywhere, and that she had cleaned up the flat before making that telephone call.
"All of these things were lies. Bethany Hill had not died as a result of cutting herself - she had been brutally, brutally murdered.
"She [Woods] lied because she was one of the two people who took part in the killing and the other person was the defendant Jack Williams.
Mr Linehan said the pair had "set about trying to cover up the truth about what they did" from the moment of the 999 call.
The court heard that Miss Hill, who was brought up in Bidford-on-Avon, had a brief relationship with Williams as a teenager.
She then moved to Stratford to begin a college course, while Williams, also from the Bidford area, met Woods and moved in with her.
Before the alleged killing, the court heard, Miss Hill had also moved into the flat in Hertford Road, using the bedroom, while Woods and Williams slept in the sitting room.
The trial continues.
A woman was tied up and "brutally murdered" by her ex and his partner, who then tried to pass the killing off as a suicide, a jury has heard.