The mother of Mark Duggan, whose shooting by police triggered last summer's riots, was given false hope that her son was alive after officers failed to inform the family of his death.
The apology was revealed after the Independent Police Complaints Authority (IPCC) upheld a complaint by the family that neither Scotland Yard or the IPCC formally notified them.
Duggan was shot and killed by Metropolitan Police officers on 4 August in Tottenham, north London.
The IPCC is still conducting a separate investigation into the full circumstances of the shooting. But it also looked into the Duggan family's complaint that they were not formally notified of his death by either the police or the IPCC.
IPCC commissioner Rachel Cerfontyne said today: "The investigation is complete and has found that Mr Duggan's parents were not informed of his death by the Metropolitan Police Service, whose responsibility it was, and I have upheld that complaint."
The Met's North Area Commander Mak Chishty said: "We recognise that it was the responsibility of the MPS to keep the family informed immediately following the shooting and up until it was handed over to the IPCC family liaison managers.
"We acknowledge and apologise for the distress caused by not speaking directly to Mark Duggan's parents Pamela Duggan and Bruno Hall.
Cerfontyne also apologised for the way the IPCC dealt with the family. The Met and the IPCC were criticised in the wake of the shooting over their contact with the Duggan family.
The family lodged a formal complaint about this in September.
Cerfontyne said that a police family liaison officer had spoken to two members of Duggan's family at the scene and on the night of the shooting. The officer told the IPCC that he had confirmed to them with '99% certainty' that the man who had been shot by police was Duggan.
The officer said the family members had asked the police not to go to the Duggan family home to formally notify his parents because it would be too much of a shock for them and said that they would do it themselves.
But Cerfontyne said the two family members, who had introduced themselves as his sister and his partner, "are categorical that neither of them told the family liaison officers that the police should not visit Duggan's parents to tell them the news of his death, nor did they say that they would inform his parents themselves.
"Indeed, both have said that they left the scene uncertain that the dead man was Mark Duggan, so in their view, they would not have been in a position to deliver such news to his parents."
The IPCC took over family liaison on 5 August and was told by the MPS that Duggan's parents did not want direct contact.
Cerfontyne said: "In the aftermath of Mr Duggan's death, his family were very confused and wanted to know what had happened to him. They did not understand the role of the IPCC, nor that the organisation was separate from the police.
"It would have greatly assisted them if a senior representative of the IPCC had visited the family home to introduce the organisation and explain its role.
"With the benefit of hindsight, the IPCC should have explored the family's wishes in more depth ... Mark's mother told us that she was receiving conflicting messages from various people in the community and the lack of formal notification allowed her to hope that the worst had not happened.
"As she told me: 'A mother's worst nightmare is the police coming to your door to tell you that your child is dead. Because this did not happen, I believed the worst had not happened'."
Cerfontyne went on: "What is clear from this case is that a grieving family, suffering from shock, felt badly treated by the police and the IPCC.
"The MPS has apologised to the family for the way in which Mr Duggan's parents became aware of his death and I have told them how sorry I am that the IPCC did not provide more support, nor visit them the day after Mr Duggan's death."