Murder detectives are questioning a 34-year-old woman on suspicion of murder after the man was found stabbed just before 6pm.
Paramedics and London's Air Ambulance were called to Chestnut Avenue, Forest Gate, at about 10.50pm on Monday but they were unable to save the male victim.
A 20-year-old stabbed while in the city's North Common late Saturday afternoon is expected to survive. We await formal identification.
A woman in her 20s has been arrested in connection with the Colindale attack.
The attack reportedly occurred inside the perpetrator's family home on Sudbourne Road in Brixton, and a man in his 20s has been arrested on suspicion of murder.
A female, believed to be aged in her 30s, was found suffering from stab wounds.
The teenager was pronounced dead at the scene just over half an hour later.
Post mortem examinations on the bodies of both the victims are expected in "due course", the Met said. It is believed the two knew each other.
KGM police immediately took action as carried out raid and arrested accused Kanji Kolhi and recovered from him involved sharp knife.
The two deaths bring the number of murders in London so far this year, where the Metropolitan Police have publicly released details, to around 59.