Reese Witherspoon is reflecting on Walk the Line. The actress -- who won the Best Actress Oscar for her role as June Carter -- took to Instagram to celebrate the film's 15th anniversary. Witherspoon posted a photo of herself and Joaquin Phoenix as the iconic Johnny Cash, laying on a couch.

"Wow! Today marks 15 years since the release of #WalktheLine 🎶 Playing the role of June Carter was one of the most rewarding experiences of my lifetime," Witherspoon began. "From the stunning costumes created by @ariannephillips to recording all of those classic country songs with T. Bone Burnett, to the incredible scenes written and directed by James Mangold, I felt completely transformed into an authentic country artist 🌟."

She then shared how she "will never forget the proposal scene... how Joaquin looked with the light beaming behind him asking June to marry him in front of a full audience."

"You could hear a pin drop. Thank you to the entire cast and crew for bringing Johnny & June's love story to life.🎙," she concluded.

ET was with Witherspoon and Phoenix as they brought Cash and Carter's love story to live.

"I grew up in Nashville, Tennessee, so I'm sort of a Southern girl and it's very daunting playing a well-known country singer," Witherspoon told ET in 2005. "Yeah it was scary!"

Phoenix added, "John was a fan of Gladiator and he asked if I'd like to come to dinner."

The actors got to visit the country singer and his wife's massive lakeside estate outside of Nashville, Tennessee. Carter even gave ET a personal tour of the estate back in 1982.

"They were very loving and warm people, so you felt a lot of their warmth in their house," Witherspoon noted. "It's a beautiful place and filled with memories."

See more in the video above.

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