The investigation into Madeleine McCann's disappearance could finish in the next few months.
Scotland Yard boss Sir Bernard Hogan-Howe said investigators are following one remaining line of inquiry and unless any new evidence comes forward, that will spell the end of the British probe.
Madeleine vanished at the age of three while on holiday with her parents in Portugal in 2007 and despite a high-profile hunt, no trace has ever been found.
Speaking on LBC, Sir Bernard said: "There's been a lot of investigation time spent on this terrible case.
Read more: Madeleine McCann's parents lose Lisbon libel case on appeal
"It's a child who went missing, everybody wants to know if she is alive and if she is where is she, and sadly if she's dead then we need to give some comfort to the family.
"It's needed us to carry out an investigation together with the Portuguese and other countries have been involved.
"There is a line of inquiry that remains to be concluded and it's expected that in the coming months that will happen."
The Home Office has granted £95,000 funding to keep the investigation - which now only has a handful of officers working on it - going for another few months.
Sir Bernard said: "The size of the team has come down radically, we are now down to two or three people in that team, at one stage there were about 30 officers in it.
"There is a line of inquiry that everybody agrees is worthwhile pursuing."
Read more: Madeleine McCann could be found alive, say detectives investigating her abduction
When asked when the probe, called Operation Grange, will end, the Met chief added: "At the moment it would be at the conclusion of this line of inquiry unless something else comes up.
"If somebody comes forward and gives us good evidence we will follow it. We always say that a missing child inquiry is never closed.
"First of all, the line of inquiry that is being pursued, that obviously is important and it is important that is resolved, and I think it will be.
"If something new comes forward we will investigate it, but that line of inquiry probably at the moment is the conclusion of this inquiry."
Hopes were high when the UK investigation into the little girl's disappearance was launched in 2011, with Scotland Yard detectives later highlighting a sex offender who had targeted British families with young children staying in villas in the same area where Madeleine was last seen.
Despite no obvious progress since then, last week Detective Chief Superintendent Mick Duthie, who is head of the force's murder squad, remained optimistic.
Read more: Madeleine's kidnappers did not take her 'a million miles' from Algarve, says Kate McCann
He said: "There is ongoing work. There is always a possibility that we will find Madeleine and we hope that we will find her alive."
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