A neighbour heard screaming as a man was stabbed to death in a nearby flat.

But when she opened her door to see what was happening, she was told it was the sounds of “good sex”, a court heard.

Kaydon Prior is accused of murdering love rival Harrison Tomkins in a jealous frenzy after finding him in bed with his ex.

Jurors were told Prior burst into Alicia Parrin’s room where he pinned Mr Tomkins, 25, to the bed, stabbing him ten times with a 16cm long, serrated hunting knife on August 13.

Prior, 23, had cut short a birthday night out in London with his friend Jason Curtis, 22, and the pair travelled to Miss Parrin’s address in Arthur Road, Ifield, Crawley.

He took “violent and angry objection” to finding out she was out in Crawley with another man that night, Lewes Crown Court heard.

Read more: 'Controlling' man storms ex-girlfriend's flat and stabs new lover, murder trial hears

Alan Gardner KC, prosecuting, said the neighbour came out of her flat after hearing Miss Parrin, 20, screaming, but Prior told her it was just the sounds of “good sex”.

Mr Gardner said: “He did not appear panicked, she thought he seemed calm but rather cocky.”

When emergency services arrived, Miss Parrin was covered in blood.

She told police Prior had attacked them after tearing the duvet off the bed.

“He just ran in and he was just stabbing him and his friend was there as well,” Mr Gardner said.

“She saw a figure run into the bedroom. She immediately recognised him as Kaydon Prior.

“He was shouting something. She remembered the duvet being pulled off the bed.

“Harrison was wearing only his boxer shorts. He was vulnerable, defenceless and completely unprepared for the murderous attack which followed.

“Somebody turned the light on. His side of the bed was covered with blood.

“She then realised that Kaydon Prior had been stabbing Harrison, not just punching him.

“Alicia tried to get to Harrison to help him but Kaydon Prior grabbed her hair and dragged her towards the bedroom door.

“Kaydon Prior then punched her on the head whilst holding her hair. He said ‘I should stab you too’.”

Miss Parrin said Prior had been violent and controlling during their year-long relationship.

She moved into her own flat and ended the relationship the day before her first night out with Mr Tomkins, who was a lifeguard.

“It is the prosecution case that Kaydon Prior was an intensely jealous individual who took extremely strong objection to Alicia Parrin being with anyone other than him,” Mr Gardner said.

“The prosecution say that it was a combination of Alicia Parrin declaring her relationship with Kaydon Prior to be over and his reaction to hearing that she was spending the night with another man at her flat which led to him taking a knife and launching a murderous attack on that man, Harrison Tomkins.

“One of the blows from Kaydon Prior’s knife penetrated his aorta, the body’s main artery, causing very rapid and catastrophic blood loss leading to rapid collapse.”

Police found Prior’s DNA on the knife, which jurors heard was dropped in the bedroom, and a bag of clothes stained with Mr Tomkins’ blood at Prior's flat in Hazelwick Avenue, Three Bridges.

Police found Curtis hiding in bushes near the flat and arrested him.

“The prosecution case is that these two defendants, acting together, murdered Harrison Tomkins,” said Mr Gardner.

“Kaydon Prior did so by wielding the knife which inflicted the fatal injuries.

“Jason Curtis assisted and encouraged him in his murderous enterprise, up to and including following Kaydon Prior into the bedroom and watching as he delivered blow after blow to the defenceless Mr Tomkins with the knife.

“It was only some way into that assault that Jason Curtis left the room to await Kaydon Prior outside.”

Prior and Curtis, of Lairdale Road, Lambeth, London, deny murdering Mr Tomkins.

Prior also denies beating Miss Parrin and carrying an offensive weapon.

The trial continues.