A neighbour who lived next door to Melbourne's house of horror where a pregnant woman was allegedly murdered and her lover decapitated and his head left on a spike has relived the horror scene.

Homicide detectives probing an alleged double-murder in Melbourne's southeast are dealing with a house of horror after they discovered a man's decapitated head spiked on a stick.

A neighbour who lived next door to Melbourne's house of horror where a pregnant woman was allegedly murdered and her lover decapitated and his head left on a spike has relived the…