Ash Barty has revealed the “red-flag” moment she knew her stellar tennis career had to end as, for the first time, the former World No.1 shares the real story behind her shock retirement earlier this year.

And it happened not on a court, but, of all places, on an exercise bike – months before she would publicly bow out, following her stunning final victory at the Australian Open.

In an entirely out-of-character move, the typically determined Barty was in the middle of a training session that she normally relished, when she did “something I have never done before”, by quitting mid-ride.

“I don’t quit. Ever,” she discloses. “I’m physically capable but cannot be knackered. This sounds like a little thing, but it’s not – it’s a clear red flag.”

The fascinating insight is one of many in Barty’s compelling autobiography My Dream Time, which finally answers questions the sporting world has been searching for since the then-25-year-old announced her surprise departure from the sport in March.

It is a tale of many threads, which will intrigue not simply sports fans, but mind gurus – because there is another from the moment Barty secretly decided “I’m done’’, a mountain of pressure floated off her shoulders and she stormed through her final Australian summer undefeated, becoming the first Australian female in 44 years to win their home Open.

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The aborted bike session drove home to Barty that, having claimed her heart’s desire by winning Wimbledon in 2021, a flame inside had dimmed and the furnace would never again rage as it once did.

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“Winning Wimbledon was the single thing I wanted my whole career,’’ Barty said when we caught up to discuss the book.

“The ceremony is still a blur to me. It was almost as if it was like an out-of-body experience.’’

But in the following months, one thing clarified undeniably. She was no longer feeling inspired. Indeed, the prospect of training, touring, playing all over again felt “pointless”.

Covering this period in My Dream Time, Barty writes, “I see now that all sport is mountain climbing. We set our sights on a summit and, step by step, we trudge towards that peak … But what do we do when we reach the pinnacle – when we finally win our Grand Final or our World Cup or our Wimbledon? Do we stop, sit, enjoy the view and breathe? Do we take the time to appreciate what we’ve done, and move on to something new? No. In sport, we simply return to base camp every year and begin the journey of attempting to summit once again.”

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Barty didn’t want to begin the climb again. Of course she kept showing up, working with her incredibly tight-knit team; sometimes she would playfully quip “Think this’ll be my last summer, guys” and they would laugh along. Deep down they knew what she knew – her desire was gone. But feeling flat was one thing. Retiring at 25 as world No 1 and reigning Wimbledon champ quite another.

Her team had one collective thought: “She couldn’t … could she?”

Beyond the jokes and asides, there were serious conversations.

A key moment came when Barty was signing posters and caps at the Gold Coast home of her manager Nikki Mathias, whose husband Ben was Barty’s hitting partner.

“I don’t know what I’m playing for anymore. I think I’m done … I have got nothing left, no spark,” Barty told him.

Ben seized the moment to say the one thing she hadn’t done was win a hardcourt slam - and told her to “just go and win the Australian Open. Then retire.” Barty says she liked the idea, took the challenge and away she went.

It was then that an extraordinary change came over Barty - the other key part of her retirement story, which has remained secret until now.

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Throughout her career she had suffered periodically under the pressure of tennis, at times grappling with depression, with the weight of expectation, on occasion falling to pieces when it all became too much - a narrative she enlarges on in My Dream Time.

But in late 2021, secure in the knowledge that she was done, with just one final challenge left, Barty says she changed: she stopped worrying about things, her emotion tapped off, on court she became almost robotic.

Feeling “cavalier’’ and “carefree’’, she started to play “imperious’’ tennis, while allowing herself to be more lighthearted between matches. And in this blissful “flow state’’ she trampled the world and dropped just one set on the way to storming through the Adelaide International then defeating Danielle Collins in the Australian Open final.

In her own words, when she stopped climbing up the mountain, the mountain came to her.

And on the way, even before the final, Barty made the biggest call of her life.

The morning after her second round Australian Open win over Lucia Bronzetti, she went walking with her mind coach Ben Crowe and his pet spanador and reached – in her mind, if not publicly – the point of no return.

“I had a chat with Crowey and that was when I knew for sure I was done,’’ Barty said.

“I was excited and nervous and super keen for what would come next. In the time before I announced it I did become stressed because you wonder whether you have done the right thing but I am very happy with my decision.’’

Barty also revealed that she had planned a dream hometown final farewell appearance for April this year, playing in a Fed Cup (renamed the Billie Jean King Cup) tie in Brisbane. But the Ukraine war changed everything, and on March 12 Barty was told the fixture had been cancelled. “Just like that, my career is over.”

Another extraordinary thing about Barty’s retirement was that some team members knew she was close to quitting months before she announced it; yet they are such a tight group not a whisper of it reached the public domain.

No-one blabbed. Had it been a football player the secret might have lasted a day.

“It was not our intention to keep it secret – I have tried to steer away from that word – so much as enabling me to do it on our terms,’’ Barty said.

“Only a dozen people knew and most of them kind of found out the day before I announced it. I have done a lot of things against the grain in my career and this was probably another one of those.’’

Five days before she announced the decision in March she met with her old doubles partner and good friend Casey Dellacqua to film a retirement video.

Six minutes and six seconds of it went to air but they chatted on camera for two and half hours, shedding many tears along the way.

Once she announced her retirement, Barty switched on the “do not disturb” on her phone and messages flowed in from the likes of Adam Scott, Hugh Jackman, Anthony Albanese, Scott Morrison and countless other big names and old friends.

She only took one call – from Evonne Goolagong Cawley.

My Dream Time is a fascinating look behind doors that Barty and her team usually keep firmly closed.

There were times when Barty shed tears in the book interview process as she revealed emotional, previously untold stories about her three Grand Slam triumphs, her ultra-tight family, the brutal isolation of being a teenager on tour, her switch from tennis to cricket mid-career, winning Wimbledon with a 10cm tear in her abdomen and much more.

“I tried to keep it raw and honest and not hide anything,’’ Barty told News Corp.

“We put it together in a way where we tried to let everyone in.’’

One of the main takeaways is that Barty’s remarkable journey – from teenage star into temporary retirement then back to glory - suddenly makes sense because she explains the reasons behind every shock detour.

You can understand why she needed a break from tennis after the stresses of starting her touring life at 13 included being left alone at a tournament in the Netherlands when her Australian touring partners moved to the next venue without her because she was still in the draw.

Barty was so upset she cried every time she hit a winner in her final match and sighed with relief when she hit the net, deliberately losing so she could link up with her squad mates.

But you could also understand why she returned to the tour - because she felt she had not quite done her talent justice.

“Those early years were tough and certainly forced me to grow up. It was probably not what I thought I was signing up for. Would I do it again? Maybe not but I met some of my greatest friends in that period.’’

So, could there be a third comeback? No, insists Barty, who has married her sweetheart Garry Kissick and returned to the quiet life at her new house in Springfield, Ipswich. Nor are the whispers she may consider a career as a golf professional true.

“The last six or seven months of my life have been everything I have ever wanted. I’m loving the way my life is at the moment. I won’t even be estranged from the tennis world and the other day I had a hit with some of the young girls … but I just won’t be out there for me.’’

My Dream Time: A Memoir Of Tennis & Teamwork by Ash Barty will be published by HarperCollins on November 2 and is available to pre-order now.