An Iraq war veteran has been found guilty of murdering a Britain’s Got Talent finalist by stabbing her more than 70 times.

Desmond Sylva, 41, attacked Simonne Kerr, 31, in a violent rage at his flat in Clapham, south London, on 15 August last year.

The former soldier, who served in Iraq and Kosovo, admitted manslaughter but denied murder, citing depression. However, the prosecutor, Oliver Glasgow QC, told jurors it was an all-too-familiar case of “sexual desire, appalling violence and desperate lies”.

He said: “He wanted to restart a sexual relationship with Simonne Kerr. When he did not get what he wanted, he could not control his anger and he exploded.”

Sylva made no reaction as the jury delivered its guilty verdict after three days of deliberations at the Old Bailey.

The judge, Wendy Joseph QC, adjourned sentencing until 28 June.

Simonne Kerr with her son Kavele, who died of sickle cell disease. Photograph: NHS press office/PA

Kerr, whose six-year-old son, Kavele, died of sickle cell disease, was part of the NHS choir B Positive on the ITV talent show.

She had previously met Sylva through the dating app Tinder and arranged to visit his flat after finishing her shift at Guys and St Thomas’ hospital on the morning of 15 August.

Sylva attacked her in bed with a 20cm kitchen knife, slashing her throat and repeatedly stabbing her face and neck. Afterwards, he called 999 and said: “I’ve just committed a murder. I’m ex-army and I’ve got lots of mental health issues.”

Glasgow told the jury: “It is hard to imagine how terrifying the last few minutes of Simonne Kerr’s life must have been as she struggled to prevent the man who was supposed to care for her from murdering her.

“The moment she realised the man who had been pursuing her wanted more than a relationship and in fact wanted to kill her must have been utterly horrifying.”

Sylva had a history of depression, bipolar disorder and post-traumatic stress disorder, and had problems controlling his temper, jurors heard. Before joining the army, Jamaican-born Sylva had cut his neck while working in a bakery.

The divorced father of one served 10 years in the Royal Regiment of Fusiliers before being discharged on medical grounds.

In 2010, Sylva throttled his mother, Patricia King, telling her repeatedly: “You’re dead,” jurors heard. King reported the assault to police, but later withdrew the complaint because he had been depressed and suicidal.

Sylva’s ex-wife had also accused him of being violent, but jurors were told the allegation was unproven.

Sylva was admitted to hospital on 9 August last year after taking an overdose.

The day before the killing, Sylva, a security guard, told his brother he feared he would kill himself or someone else.

Giving evidence, Sylva said: “I did not mean to kill her. I had deep feelings for her. When I slashed the knife across her throat at that split second I thought I had a mental breakdown.”

The psychiatrist Dr Philip Joseph told jurors Sylva suffered from moderate depression, but did not report having flashbacks of Iraq during the killing. He said Sylva had told him the pair argued and Kerr called him a “good for nothing” before threatening him with a knife.

The defendant claimed he must have lost control as he disarmed her, but said he could not remember the stabbing.

Joseph questioned whether it had anything to do with being depressed, suggesting Sylva was “predisposed to violence”. He added: “It may be his attack on Simonne is all to do with battling with feelings and angry outbursts leading to an enraged state of mind.”