Arthur Simpson-Kent, partner of former EastEnders actress Sian Blake entered guilty pleas before a judge for murdering Ms. Blake and their two children.
The guilty pleas were sent to Mr Justice Singh at the Old Bailey via video link from Belmarsh prison in the UK.
Ms Blake, 43, Zachary, 8, and Amon, 4, were found at the family home in Erith, London, in January after being reported missing on 16 December. Outside court, Ms Blake's sister Ava said the family were "really relieved".
Simpson-Kent, a hairdresser, was arrested at Heathrow Airport in February after being extradited from Ghana. He left the UK days after Ms Blake and her sons went missing but was later arrested on a beach in Ghana by local police. The arrest came after locals recognised him from a photo shared on social media and tipped off the authorities.
The bodies of Ms Blake and the two boys were found four days after they were reported missing. A post-mortem examination found Ms Blake and her sons died from neck and head injuries.
She played Frankie Pierre in 56 episodes of EastEnders between 1996 and 1997 and had been living with motor neurone disease before she died.