If your child disappeared, how long would you hold out hope of finding them alive?
No parent wants to accept that their child may be gone for good, but after a certain point it becomes hard to hold out hope.
In a new interview, Gerry McCann, father of missing girl Madeleine McCann, says he still believes he could be reunited with his daughter someday.
"Kate was screaming, "˜Madeleine's missing, she's gone.'"
Gerry and Kate McCann from Leicester, England took their young children - three-year-old Madeleine and her two-year-old twin siblings - on a group vacation to Portugal in 2007.
The McCanns stayed at the Ocean Club apartments in Praia da Luz, and spent most nights eating with the other parents in their group at a nearby restaurant.
But on the night of May 3, Kate returned to their apartment from dinner to a horrible discovery: Madeleine had vanished without a trace.
In a new interview with BBC Radio 4, Gerry described the painful moment he first realized his daughter was gone.
"Kate was screaming, "˜Madeleine's missing, she's gone,'" he said.
"And I was like she can't be gone... and (I remember) running in and checking the bedroom but obviously she wasn't there."
Even in the first minutes of Madeleine's disappearance, Gerry says he believed his daughter had been abducted, and the realization left him feeling helpless.
"I think I remember just being in the bedroom distraught, the two of us," he said.
"Just completely distraught. I was almost feral, the reaction and the pain, feeling helpless, alone, alone together but it [was] just the most painful realization and I couldn't get the darkest thoughts out of our minds that somebody had taken her and abused her."
But despite his dark thoughts, Gerry says is still "convinced" that Madeleine is alive.
"It's almost like an instinctive reaction... it's just a feeling... but I do feel we will be reunited," he added. "I just want to hug her and hold her and cry... a lot."
"We're not the ones that have done something wrong here."
The hunt to find Madeleine has continued nonstop since the night she went missing, and has grown to involve police departments in Portugal, the UK, and countries around the world.
But the initial investigation by Portuguese investigators, which targeted tourists in the McCann's own vacation group, made little progress.
At one point, the McCanns themselves were treated as suspects in their own daughter's disappearance. They even pursued a libel case against a Portuguese detective who questioned their version of the night's events in a book.
"Once the spotlight had turned on us I said to Kate we needed to leave," Gerry remembered. "That whole journey to the airport was just like something out of a horror movie. A nightmare."
"We're not the ones that have done something wrong here," Kate said. "It's the person who's gone into that apartment and taken a little girl away from her family."
Portuguese detectives eventually named four suspects in Madeleine's disappearance in 2013, but after being interviewed by police no charges were filed against any of them.
The McCanns often described their frustration with the Portuguese investigation, and Gerry complained they were too slow to respond the night Madeleine went missing.
"I remember asking the police to get helicopters and heat seeking equipment and the thought somebody could be across the border into borderless Europe, driving her. Or Africa "“ the ports are a couple of hours away. I remember thinking "˜get the borders closed,'" he recalled.
After the Portuguese case stalled, police from Scotland Yard took over, launching what they called Operation Grange.
British police have since interviewed 60 people while following more than 560 leads. They have also helped investigate almost 9,000 Madeleine sightings in more than 100 countries (almost all of which have been ruled out).
Theories And Wild Hopes
Scotland Yard has claimed that Madeleine's case has all of the signatures of a planned abduction.
The McCann's have their own theories, including that someone might have seen a note describing when they would be out to dinner, and planned to abduct Madeleine at that time.
There were also reports of burglaries and fake charity scams near the apartments that police believe could be linked to the abduction.
For years, the most substantial lead was a man seen carrying a child in pajamas towards the ocean just as Madeleine was reported missing.
An artist's impression of the mystery man was even released by police. But they now believe he was probably an innocent parent, who had picked his child up from the resort's nursery the night of the abduction.
While a small four-person team continues to investigate Madeleine's disappearance in Portugal, they are waiting for more funding from Britain's Home Office to continue the search.
So far, police have already spent more than $15 million on the case, but they warn that if their application is denied the trail could turn cold forever.
Whether the funding is approved or not, the McCanns will continue to hold out hope for their daughter - who would be 15 today - to return to them.
Gerry revealed that Madeleine's childhood room is also waiting for her, with glow-in-the-dark stars still stuck on the ceiling, her clothes hanging in the closet, and unopened birthday presents waiting to be unwrapped.