It’s been 40 years since Olivia Newton-John, 69, and John Travolta, 64, joined forces to play good girl Sandy and bad boy Danny in 1978’s Grease. Together they made movie history (the film earned almost $400 million worldwide) and also launched a friendship that has lasted four decades.
“We did something life-changing, making that film,” Newton-John tells PEOPLE. “[At the premiere] you got the feeling from the energy that something was happening. It was a huge response. I feel grateful to be a part of that and to have worked with him. We’ve stayed friends ever since.”
To mark the occasion, Paramount recently released a 40th anniversary DVD edition of Grease, which includes a fully restored version of the film and bonus features.
Travolta, who was just 23 when he starred in the film, says he and Newton-John have been by each other’s side through the best and worst times of their lives. The actor wed actress Kelly Preston in 1991 and is dad to Ella Bleu, 18, and Benjamin, 7; their oldest son Jett died of a seizure in 2009. While Newton-John, who has been married to John Easterling since 2008 and is the mom to Chloe, 32, revealed last spring that she was battling
breast cancer again after first being diagnosed in 1992.
“[In tough times] John always reaches out to me,” she says. Travolta echoes the sentiment.
“When you share that kind of meteoric success—and nothing has been able to exceed it—you share a bond,” he says. “I’ve been through her having a child, getting divorced, losing her sister. She’s been through my getting married, having children. It’s wonderful and full of shared memories.”
For more on Travolta and Newton-John, pick up this week’s issue of PEOPLE on stands Friday and PEOPLE’s 40th Anniversary Grease special issue July 6.
And while the duo both passed on Grease 2, they costarred again in Two of a Kind in 1983, which unfortunately bombed. “You never know with films,” says Newton-John. Then in 2012, they released the album This Christmas, benefiting her Olivia Newton-John Cancer Wellness & Research Centre and his Jett Travolta Foundation for children with special needs.
Even with Newton-John living in Australia, she says the two continue to keep in touch and often text.
“Olivia’s quite a spectacular human being,” adds Travolta. “She’s worthy of good friendship.”
With reporting by Allison Adato