Fifteen months after she announced her breast cancer had returned and spread, mystery surrounds the sudden cancellation of Olivia Newton-John’s two-date Australian tour next month.

The spoken word tour was announced only three weeks ago.

On August 13, the four-time Grammy winner tweeted that she was “excited to see everyone” at her ‘In Conversation’ gigs in Melbourne and Sydney.

Newton-John was due to speak on stage with journalist Ray Martin, in what the show’s promoter Lateral Events described as Newton-John “re-living her extraordinary life.”

But on Wednesday, a short announcement on the promoter’s website confirmed “with regret” the shows are off for “reasons beyond our control”.

It promised full refunds to ticket holders.

“We are very sorry about this – cancelling shows is the last thing we like to do.”

The shows had apparently been selling strongly, with inquiries for the Melbourne date being directed to an official resale site.

Lateral Events did not reply to The New Daily’s request for comment about what led to the cancellations.

Worried fans noted on social media that the news “cannot be good.”

This cannot be good I saw a picture of her & she looks so thin & frail

— CatSlave (@Thunderbird_65) August 22, 2018

Last May, Newton-John postponed her June 2017 US and Canada tour dates after going public with news that the breast cancer she was first diagnosed with in 1992 had spread to her spine.

She had been suffering back pain and “was sort of surprised” to hear her cancer had returned.

“In my mind, it was over. I had finished with it,” she told the US Today show in September.

“I’d be lying if I said it wasn’t scary but I intend to be healthy,” she told 60 Minutes last September.

Saying her husband John Easterling was her “rock”, she told Today that she avoids reviewing her prognosis because it was “depressing”.

She vowed she wasn’t “going to be one of those statistics.”

Said Newton John, “Having [cancer] again, I thought to myself, ‘I’ve done this before. You know, I got through this before and I can do it again’.”

The singer had timed her Australian speaking events to coincide with the annual Wellness Walk and Research Run to fund-raise for her Olivia Newton-John Cancer Wellness and Research Centre in Melbourne.

The star will still take part in the walk, a cancer centre spokesperson confirmed to The New Daily on Wednesday.

“We encourage her many fans to join the event and take the opportunity to walk with her,” said the spokesperson.

Newton-John’s last public appearance was a week ago on August 15, when she and co-star John Travolta busted some dance moves at an Academy of Motion Picture Arts and Sciences’ screening celebrating the 40th anniversary of Grease.

Travolta, 64, said at the event that he had personally insisted Newton-John be cast in the movie.

“If you remember that album cover of Olivia with that blue shirt on, with those big blue eyes staring right at you, every boy’s, every man’s dream was, ‘Oh, I’d love for that girl to be my girlfriend’,” the actor told the audience.

“When I had the privilege to have input on the casting, I said, ‘There is no other person in the universe other than Olivia Newton-John to play Sandy. You must cast her’. So I held tight, didn’t I, and I got my way.”