A woman was found dead in south London less than an hour after police discovered the bodies of her husband and two young boys more than 80 miles away.
Scotland Yard said a murder investigation had been launched after the woman, believed to be in her 40s, was found dead with stab wounds at her home in South Road, Twickenham shortly before 6pm on Monday.
Detectives attempted to trace her husband, 57 and two boys, aged seven and 10, and were contacted by Sussex Police officers who had found the bodies of a man and two children at Birling Gap seafront, in Eastbourne, East Sussex, at around 5pm that day.
A Metropolitan Police spokesman said: "Whilst formal identification awaits, police believe that they are the deceased woman's immediate family."
No arrests have been made and the Met said officers are not looking for anyone else in connection with the investigation.
A vehicle was recovered near the seafront scene by Sussex Police and a crime scene remains in place at the Twickenham address.
Post-mortem examinations have yet to take place and next of kin have been informed.