25/08/2017 9:49 AM AEST | Updated 25/08/2017 3:23 PM AEST

Missing Boy William Tyrrell 'Probably Dead': Judge

It's been revealed Tyrrell was in foster care when he disappeared.

Supplied / NSW Police
The then three-year-old Spiderman fan disappeared from outside his foster grandmother's home in September 2014.

A NSW Supreme Court judge has for the first time acknowledged the "tragic probability" that missing boy William Tyrrell is "no longer alive".

But NSW police say the search for the missing boy remains "very much ongoing".

It's been almost three years since William, then aged 3, vanished while visiting his foster grandmother's home in Kendall on the NSW mid-north coast on September 12, 2014.

The NSW Homicide Squad told the Daily Telegraph that police were still pursuing "numerous lines of inquiry" before they would abandon the search.

"It is important to note that at the time of his disappearance, William was living in a loving home and was well cared for — there is no indication his family status played any part in his disappearance," a Homicide Squad spokesperson said.

"We are reminding the community that a young child is still missing and our focus will always be on bringing William home."

Justice Brereton's admission of the likelihood of William's death comes as he ruled that Tyrrell's being in foster care at the time of his disappearance was a matter of "legitimate public interest" and therefore should not be suppressed.

The new details were made public by Channel 9's A Current Affair on Thursday night, after three judges from the Court of Appeal upheld his ruling.

For three years, the fact that William was a foster child has been concealed.

The Department of Family and Community Services has repeatedly threatened journalists with criminal charges if they revealed William was in the care of the state when he went missing, according to Channel 9 News.

Justice Brereton ruled that the new information of William being in foster care may not assist the investigation into William's disappearance, but would be unlikely to hinder it.

There is no suggestion that either William's foster family or his biological family were involved in his abduction or know his whereabouts.

Supplied / NSW Police
William Tyrrell

Few clues as to what happened to William after he disappeared while playing outside his foster grandmother's home have been uncovered.

It was initially thought he may have run off into nearby bushland, but a wide-scale search by investigators and volunteers failed to find him.

Later, NSW Police Homicide Squad said they were pursuing the possibility that William fell into the hands of a paedophile ring.

His case was referred to the NSW Coroner in September 2015, but police at the time said this was "standard protocol" and thousands of people still held out hope he would be found alive.

Fairfax Media
William Tyrrell went missing from his foster grandmother's backyard in Kendall, NSW.

In September 2016, an unprecedented $1 million reward was offered for information leading to William's recovery as part of the 'Where's William?' campaign.

William would have turned six years old in June.