Geri Horner's brother Max Halliwell has died suddenly at the age of 54 following a collapse.
Max suffered the incident last week and was taken to hospital in Watford, where he died while in intensive care.
A spokesperson for Hertfordshire Constabulary said: "Police were called at 9.40am on Wednesday 17 November to report the concern for welfare of a man at a residential property in Berkhamsted.
"Officers, along with the East of England Ambulance Service, attended the scene.
"The man was located and taken to hospital for treatment, where he sadly later died. His death is being treated as non-suspicious and will be referred to the coroner."
A source close to singer Geri, 49, added to The Sun: "This is the most awful, devastating, heartbreaking news and Geri is utterly broken by it.
"It has been a terribly traumatic time since the moment she heard Max had been taken to hospital, and the worst outcome which everybody close to the family hoped might not be.
"They are all rallying together but she barely knows what to say or think just now - she loved him dearly."
The cause of Max's death has not been disclosed.