Karanbir Chema, 13, known as Karan, slipped away 10 days after a piece of Cheddar was hurled at him at school in July 2017.
Mum Rina Cheema, 53, made the devastating decision to turn off his life support.
She has revealed how she has been “living in a black hole” since her only son’s death, describing the tragedy as “something that’s going to haunt me for the rest of my life.”
In his last picture, the schoolboy can be seen with tubes coming out of his mouth while hooked up to a life-support machine.
“It is something that’s going to haunt me for the rest of my life.”
Mum Rina Cheema on her son Karan’s tragic death
It comes after grieving Rina criticised the school, William Perkin Church of England High School in Greenford, north-west London, for “taking too long” to call 999.
Accountant Rina, from Greenford, told the BBC of her heartbreak.
“I sent him to a place where I thought he’d be safe only to find out nobody knew what they were doing. If they knew that allergies cause problems – it’s no problem giving an EpiPen.
“They could have given him an EpiPen. Or even dialled 999 straight away. He would be here with me today.”
Rina shared the picture in a bid to raise awareness of how allergies can be deadly.
Revealing her pain at turning the life support machine off, Rina told Holly and Phil on This Morning: “We didn’t want to switch it off – it wasn’t fair on his little body to go through this.
‘He smiled when the machine was turned off, they took him into another room and we said our last good byes before he was taken down and he had a smile on his face.’
She added: ‘You’re always praying for the last minute miracle his brothers and sisters and his uncles were all there beside him.’
The boy who threw the cheese, who cannot be identified for legal reasons, was arrested and interviewed by police but not charged.
He was later expelled from the school.
Rina added: “The school knew he had severe allergies and a catalogue of errors was made leading up to his death.
“But I’m not out for revenge – I want to make a change for the better.
“I’m desperate to change the system so that no other parent has to face what I’m now facing.
“My son should not have died that day. He was my only child, my world, I have been left with nothing.”
An autopsy report stated that Karan died from a brain stem injury due to lack of oxygen.
Dame Alice Hudson, executive headteacher of the Church of England’s Twyford Trust, which operates the William Perkin School, said after the inquest into Karan’s death: “We are deeply sorry that we could not save Karan.
“We completely accept the coroner’s findings about the systems we had in place at the time, and regret that they were not enough.”
The school has since updated its allergy policy and has two spare EpiPens, should any pupil need one.