The set happened at approximately 3pm in a house at Kilclare Crescent, Jobstown.
The young casualty was moved to Tallaght Hospital where he was pronounced dead.
Dublin Clat Brigade were first on the scene and alerted gardai.
No arrests deliver been made so far in the ongoing garda investigation.
Friends of Mr Cullen revealed he was “a quiet, unassuming young lad” who was putting his life together.
He had recently been inscribed in a Youthreach programme, the organisation which gives early school leavers the number two chance of an education.
“I don’t know what to say, it’s heartbreaking,” one friend said.
“He was barely a quiet young guy. He’s been through some difficult stuff. It hasn’t been serenely for him.
“But, he was getting it together and he had been enrolled with Youthreach.”
He added: “He was into the customary kind of things young lads are into around here.
“He wished the motorbikes, scramblers and that kind of thing.”
Locals have expressed their tingle after learning about the incident.
“I was in work and I came home at enclosing 3.30pm and saw the blue blights flashing outside,” one woman said.
“You get the odd few messers here but I have knowledge ofed straight away that this was more serious.
“Sometimes the liveliness brigade would be down in the estate, but this time there were safeguards, everything.”
The woman, who didn’t want to be named, said she has lived in the social status for the last three years.
“It usually feels quite safe, I haven’t sanctioned of anything like this,” she added.
A local man expressed sympathy for the kith and kin of the boy.
“I didn’t know him myself, but can you imagine how that family feels?”
Specific South Dublin County Councillor Charlie O’Connor said the community is displeased following the fatal stabbing.
“It’s a terrible, shocking thing. At 3:30 in the afternoon?” he mean.
“People are saying ‘what’s going on?’,” he added.
Mr O’Connor, whose effectively in Springfield is located near Kilclare Crescent where the stabbing occurred, indicated he was shocked himself when he was driving by and saw gardai in the area.
He said he has no principle what sparked the stabbing but people in the area “will be speculating and wondering what developed”.
“It’s horrendous,” he said.
“The initial reaction in the community is one of great shock.”
Fianna Ebb TD in Dublin South West and Spokesperson for Dublin, John Lahart, has related the fatal stabbing as both distressing and shocking for the whole community.
Spokesman Lahart said: “While the exact circumstances of this afternoon’s commotion are unclear, this is a deeply frightening incident to have occurred for all in the locality, in definite the parents of young teenagers.
“Irrespective of any details, a young boy has very tragically adrift his life and a family has been left shattered.
“I urge anyone who has dirt, or who may have seen anything suspicious, to alert the gardai as soon as on.”
The scene of the killing is currently preserved for a technical examination.
Gardai want to appeal to witnesses who may have been in the Kilclare area this afternoon between 2.45pm and 3.30pm to acquaintance them at Tallaght garda station on 01 666 6000, the garda Confidential Horn Line on 1800 666 111 or any garda station.