Ally Harris and Jessica Redmayne on their new Home and Away roles - and the battles they’ve faced

 ‘We support each other.'

In 2014, actress Jessica Redmayne's life changed forever when she came home to devastating news after a two-month stint in the Philippines on tour with a production of Alice In Wonderland.

"I'll never forget the day I returned," Jessica, 31, tells TV WEEK. "Mum ran down the driveway and said, 'Jess, everything's changed – I've been diagnosed with dementia.' I told her everything was going to be OK, but I already knew [she had it]. Now, we had it in writing."

Jessica had suspected something might have been wrong when her mother, Christine, would forget she'd made a cup of tea and leave it in the microwave, or go to the shops to buy bread and return with washing detergent. What she wasn't prepared for was just how rapid her decline would be once the diagnosis was official.

"After I returned from doing 800 Words [the comedy drama that ran for three seasons until 2018] in New Zealand, she declined significantly," she reveals. "She's been in care for four years; she has no physical mobility and is non-verbal. She completely forgot who my dad and I were five years ago."

At the beginning, visits were tough for Jess, with her mum often confusing her for a friend and thinking herself much younger than she actually was.

She'd ask, 'Where's my mum?'" Jess recalls. "One of the first times she asked, I told her, 'Your mum passed away,' and she burst into tears. I ended up telling her a white lie – that her mum had gone to the shops – but it was in her best interest."

Jess knows how proud Christine would be of her role as Harper Matheson in Home And Away.

"The worst part is that I can't share this with her," Jess says through tears.

"She took me to dancing lessons four or five times a week for almost 15 years and made all my costumes. She took me to acting lessons, modelling and everything under the sun – she was so encouraging."I wouldn't be doing this without her, and I know she would be so proud."

Jessica is now an ambassador for Dementia Australia and hopes that by sharing her story, people who've gone through the same experience will know they aren't alone. She also wants to educate others about how to detect signs of early onset dementia.

"Mum was a very vibrant, charismatic woman, but that started to diminish in her personality in her mid-50s," she explains. "She became quite insecure, particularly in her decision-making, so we knew something was wrong, but it [evidence of dementia] didn't show up in MRI scans until she was 60."

Jessica and Home and Away co-star Ally Harris have become fast friends after starting their Home And Away journey together and have leant on each other as they navigate the new experience. Ally, who was diagnosed with Attention Deficit Hyperactivity Disorder (ADHD) later in life, jokes that she's lucky to have Jessica to tell her when to show up to set.

"I had a long history of not being very productive and not understanding why," Ally, 24, says. "I felt a lot of pressure and kept asking myself, 'Why can't you follow through? Why can't you finish things?' Now, I have more of a handle on it and have become obsessed with getting lots of things done. It can be overwhelming."

Ally plays Dana Matheson, Jessica's sister's character. In a case of life imitating art, the two have what Ally describes as a "big sister, little sister" dynamic in their off-camera friendship.

"I'm so thankful I've met Jess," she says. "Throughout my career, I've met wonderful women who have helped ground me and respect myself more as an artist. She helps me articulate my needs as an actor; she really has her stuff together."

"We spend a lot of time outside of work together," Jess reveals. "Our friendship really contributes to the chemistry of the characters on the show."

Packing up in Perth and moving to Sydney for the role, Ally has left behind her partner of nearly two years. But the distance hasn't dimmed the relationship.

Honestly, it's much better than I thought it would be," she tells. "He's interstate a lot and we're very lucky that we've never played mind games or anything like that with each other, so we're very secure [in our relationship]."

Jess shares that it "hasn't sunk in yet" to be a part of the H&A legacy.

"It's such a huge part of the Australian culture," she says. "The number of people from around the world who come to Palm Beach [in Sydney's north] to watch us film is extraordinary. To be a small part of that makes me very proud."