John Travolta says Olivia Newton-John is doing ''fine'' as she battles breast cancer for the third time.

The 64-year-old actor - who starred with Olivia in 'Grease' - has revealed his former co-star is doing well, despite her ongoing battle with cancer, which she revealed in 2017 is her third time fighting the disease.

Speaking to 'Entertainment Tonight', John said: ''From what I hear talking to her she's fine. I think she even made a public announcement in her own video, [saying] that she was fine.''

John's comments come after 70-year-old Olivia took to social media earlier this month to rubbish false claims that she had just ''weeks'' to live, as she insists she's still in good health.

She said in a video on Twitter: ''Happy New Year, everyone! I just want to say the rumours of my death have been greatly exaggerated, to quote a very famous quote, and I'm doing great and I want to wish all of you the happiest, healthiest 2019 that's possible.

''Thank you all for the wonderful love and support for me and for my Olivia Newton-John Cancer Wellness Centre in Melbourne, Australia.''

The update on her condition came after she previously revealed that she'd faced a second battle with cancer in secret in 2013.

Olivia was first diagnosed with cancer in 1992 and underwent a partial mastectomy, nine months of chemotherapy and a breast reconstruction, and after she revealed the disease had returned in May 2017, she told fans in September last year this current battle was her third after the one she'd faced in private five years previous.

Despite her ongoing medical battle, Olivia won't be consumed by negativity, as she knows she's ''a very privileged person''.

The 'Physical' hitmaker added: ''There are other people out there doing much, much worse than me. I'm a very privileged person, and I'm very aware of that. I live in this beautiful place. I have a wonderful husband. I have all the animals that I adore. I have an incredible career. I have nothing, really, to complain about.''