John Travolta is ''very proud'' of Olivia Newton-John amid her cancer battle.

The 70-year-old actress is currently battling breast cancer for the third time, and her 'Grease' co-star John, 65, has gushed about her strength as she deals with stage four cancer.

He told Entertainment Tonight: ''She looks incredible. She doesn't look any different than [she did] years ago, and I'm very proud of her. I'm very happy about Olivia.''

Olivia previously insisted she feels ''lucky'', despite being diagnosed with stage four cancer.

She said: ''I'm so lucky that I've been through this three times and I'm still here. We know we're gonna die at some point, and we don't know when it is. When you're given a cancer diagnosis or a scary honest diagnosis, you're suddenly given a possibility of a time limit. So every day is a gift.

''If somebody tells you, you have six months to live, very possibly you will because you believe that. So for me, psychologically, it's better not to have any idea of what they expect or what the last person that has what you have lived, so I don't, I don't tune in.

''Every day is a gift, we don't really know how long our life is. I'm very grateful, and I intend to be here for a long time. I have much to do still.

The star was first diagnosed with cancer in 1992 and underwent a partial mastectomy, nine months of chemotherapy and a breast reconstruction.

She later revealed she had faced a second battle with cancer in secret in 2013.

And although the disease returned in May 2017, Olivia won't be consumed by negativity, as she knows she's ''a very privileged person''.

The 'Physical' hitmaker said: ''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.''