The remains of a baby have been found in the search for the missing child of Constance Marten and Mark Gordon.
Police said the body had been found in a wooded area of Brighton, close to where the couple were arrested on Monday.
“I understand that the conclusion of this search will be heartbreaking for the local community and the wider public,” said Detective Superintendent Lewis Basford.
Live updates: Baby’s body found in woodland
He said police would “do everything we possibly can to establish what has happened”.
A crime scene is in place where the body was found and a post-mortem will be carried out.
Aristocrat Marten and her boyfriend – a convicted sex offender – were detained in Brighton on Monday on suspicion of child neglect after a member of the public spotted them at a shop.
They were further arrested on suspicion of gross negligence manslaughter on Tuesday after police said they had refused to say where the baby was.
More than 200 officers have been looking for the child in allotments and woodland in and around Brighton – an area of 90 square miles.
Wild Park, in the city’s Moulsecoomb area, was among the areas being searched on Wednesday and officers were seen scouring the undergrowth and ponds.
Drones, sniffer dogs, thermal cameras and a helicopter have all been involved.
Marten, 35, and Gordon, 48, were reported missing on 5 January after their car caught fire on the M61 near Bolton.
It is believed Marten had given birth just a few days before and that the child had not received any medical checks.
Over the following days, there were sightings of them in places including Liverpool, Essex, and east London.
Before their arrest, they were last seen in Newhaven – about seven miles east of Brighton – on 8 January.
Authorities believe they were sleeping in a tent and avoided detection by using cash, hiding their faces and usually moving around at night.
CCTV from Monday night appears to show Gordon – who served 20 years in an American jail for rape – limping and using a stick to walk.
The Sun also reported that the couple visited a food bank last Wednesday but did not ask for baby products despite them being available.
Marten is from a wealthy aristocratic family with royal connections and her parents had pleaded for her to come forward.
Police were earlier given another 36 hours to question the couple.