Claire King was "in shock" when she found out about Leah Bracknell's cancer diagnosis.
Former 'Emmerdale' actress Leah - Zoe Tate on the ITV soap from 1989 to 2005 - revealed last week that she has been diagnosed with terminal lung cancer and Claire, who portrayed Leah's evil on-screen stepmother Kim Tate until 1999, was heartbroken when she heard the news.
She said: "When I heard I was completely floored, I was in shock. Leah is beautiful, radiant, sweet and kind - everyone falls in love with her. To have this happen to someone like her is heartbreaking, horrible.
"She's vegan and a yoga guru, she's fit and healthy-living. I can't believe she's been one of the unlucky ones. It's cruel - it shows what a b*****d cancer is."
While the pair were enemies on-screen they are the complete opposite in real life and became close friends.
Claire told the Daily Mirror newspaper: "A lot of people thought we didn't get on because our characters hated each other. But off-screen we clicked instantly.
"We became really good friends and saw each other through whatever life threw at us - she was always the one I would turn to when I had a problem."
Leah launched a fundraising campaign and successfully raised the £50,000 she needs to undergo potentially life-saving treatment at a hospital in Germany.
Leah previously explained her health situation on her GoFundMe page, writing: "Just over 5 weeks ago, I was feeling perfectly well, fit and healthy. Teaching yoga classes and workshops, it was a time of new beginnings: preparing to move house, youngest child fleeing the nest, and excited to be starting rehearsals for a comedy play, being back onstage, going on tour.
"But, it turns out that the universe had other plans. Life was about to be unexpectedly turned on its head.
"I began to feel breathless climbing stairs ... I just put it down to a bit of stress. My abdomen suddenly ballooned - and within a matter of a few days I looked heavily pregnant. I could barely walk or breathe. Then, one Saturday night at the beginning of September I ended up in A&E. (sic)"