The heir to a cake fortune told his friend he was considering ‘killing him’ before slitting his throat with a kitchen knife in a brutal attack, a court heard.

A “lonely” heiress told her friend she was “thinking of killing” him a few months ago, then stabbed him to death in a “frenzied attack”, a court heard.

Dylan Thomas, 24, the heir to one of Britain’s biggest business empires, is accused of slitting the throat of his flatmate William Bush in a violent attack on Christmas Eve last year.

A ‘terrified’ Mr Bush, 23, barricaded himself in his room while he slept after Thomas allegedly told him he was going to kill him just two months before the fatal attack, a court heard.

Mr Bush, described as the defendant’s ‘only true friend’, suffered 21 wounds to his neck after Thomas allegedly attacked him with two knives and cut his carotid artery.

Cardiff Crown Court was told ‘screams of terror’ could be heard coming from the street from the house during the seven-minute attack that night.

Thomas, the grandson of cake and property tycoon Sir Stanley Thomas, admitted manslaughter but denied murder, claiming diminished responsibility.

The pair initially met while students at Christ College in Brecon and lived together in Llandaff, Cardiff, at a property owned by Thomas’ entrepreneur grandfather.

The court heard how close the young men were, holidaying and playing golf together, but the dynamics of their relationship began to change in the run-up to Christmas.

Strong and athletic, Mr. Bush was a researcher who was about to move out of their shared home to set up home with his girlfriend, Ella Jeffries.

Mr Thomas was described as ‘alone’ and ‘weak’ between the two men; Mr. Bush was his only real friend.

Prosecutor Greg Bull KC said: ‘William Bush was well-liked; He was a quiet and passive man, avoiding confrontation.

‘He was looking forward to starting a new business and starting a family with his partner Ella.’

Mr Bull said: ‘Mr Thomas relied heavily on Mr Bush, but the dynamics of their relationship were changing. Mr Thomas’s attitude seemed to have changed.’

Gregory Bull KC said Thomas was ‘suffering from a mental disorder’ at the time of the attack.

But the Crown argued Thomas planned the attack by investigating the anatomy of the victim’s neck before texting him: “I need to see you before I go.”

The prosecutor told the court that Mr Bush told Ms Jeffries that Thomas once told him: ‘I thought about killing you, I just wanted to see what would happen if I did certain things.’

Mr Bush’s girlfriend told police the threat was taken seriously by the deceased, who barricaded her door while she slept.

The court heard ‘screams of terror’ could be heard from the house during the attack, which could be heard from the street.

Thomas is accused of first using the knife to stab Mr Bush in the back, then trying to ‘run for his life’, according to the investigator.

Mr Bull added: ‘It is clear that Dylan Thomas used the kitchen knife to stab Mr Bush in the chest and slit his throat, severing the main artery in his neck, resulting in Mr Bush bleeding to death.’

The black knife used in the attack, as well as a kitchen knife that was covered in blood and had its tip bent during the incident, was also shown to the jury.

Thomas told police he stabbed Mr Bush in self-defense and insisted his friend was ‘throwing a fit’.

Thomas was injured in both hands during the incident and told police the incident occurred while he was trying to disarm Mr. Bush.

Mr Bull said the prosecution accepted Thomas was ‘mentally unstable’ and had become psychotic before the murder on Christmas Eve.

He said: ‘After the murder his condition deteriorated and as a result he began being treated for schizophrenia in hospital.’

The jury heard Thomas had previously had at least one hallucination and believed Mr Bush was “threatening to drink his spinal fluid”.

He said two psychiatrists examined Thomas and disagreed on whether the act was due to psychosis, while Mr Bull suggested the “frenzied attack” was deliberate.

He said: ‘The difference between the two doctors is about what happened at the time of the murder.

‘Mr (Dilum) Jayawickrama is of the view that when you look at the evidence as a whole it shows that the accused knew what he was doing.

‘In Mr. Jayawickrama’s view, even if a man suffers from a psychotic illness, this does not necessarily mean that the act was caused by psychosis.’

The trial continues.