A 19-year-old was detained on Sunday after cops were called to the scene of a stabbing at an address in Buddings Circle, Wembley on Saturday, 15 October.
Cops, London Ambulance Service and London”s Air Ambulance were on the scene.
The 18-year-old was pronounced dead shortly before 2pm.
A post-mortem examination found he died of stab wounds.
Cops believe they know the identity of the teen but are waiting for formal identification.
His family have been informed.
The investigation is ongoing.