The father of murdered backpacker Grace Millane has died after a battle with cancer.

David Millane was diagnosed with cancer after spending almost three weeks in Auckland attending the trial for his daughter's killer.

It is understood he was told recently the cancer had spread and was not treatable.

He died earlier this week.

He is survived by his wife Gillian and sons Declan and Michael.

David Millane (centre) and Gillian Millane at Auckland High Court for the trial of Grace's murderer in November 2019, with Detective Inspector Scott Beard (left). Photo / Michael Craig

Grace Millane, a graduate in marketing and advertising, was last seen alive in central Auckland on December 1, 2018.

Her body was found eight days later in West Auckland's Waitākere Ranges, near Scenic Drive.

A man who was 26 at the time was convicted of the murder and was sentenced in February this year to life in prison with a minimum non-parole period of 17 years.

He strangled Millane to death in his central city hotel apartment.

She died on what would have been her 22nd birthday.

David Millane flew to New Zealand soon after reporting his daughter missing.

He and Gillian Millane later returned to Auckland for the trial and to see the man who killed their daughter convicted.

Police in Auckland, led by Detective Inspector Scott Beard who ran the investigation into Millane's death, worked closely with the family.

They kept them updated on the progress of the initial investigation and then helped to prepare them for the trial and supported.

Beard spoke about David Millane's death this afternoon.

"New Zealand Police wish to extend our deepest sympathy to family," he said in a statement.

"The Millane family had their lives turned upside down when David's much loved and cherished daughter Grace was murdered while visiting New Zealand in December 2018.

"Police worked closely with the Millane family as part of the investigation into Grace's murder and provided victim support throughout subsequent trial.

"Our thoughts and sympathies are with Gillian, Michael, Declan, and the rest of their whanau."

Beard said the family has asked that the media respect their privacy at this difficult time.

In a heartbreaking statement after the guilty verdict, the couple described Grace as their "sunshine".

"Grace was a beautiful, talented, loving daughter. Grace was our sunshine and she will be missed forever," David Millane said, through tears.

"She did not deserve to be murdered in such a barbaric way on her OE year."

At the killer's sentencing in February, members of the Millane family read Victim Impact Statements, appearing in court via an audio visual link from their home in Essex.

David Millane did not read a statement as he was too unwell.

The murderer cannot be named at this stage.

After he was sentenced he took his case to the Court of Appeal, maintaining his claim that Millane's death was accidental and occurred during rough sex.

The Appeal Court has not yet released its decision and the man's name remains suppressed.