The stars of Fifty Shades Freed get hot and heavy a lot, but Dakota Johnson reveals just how unsexy being behind these scenes really is.

In an interview with Marie Claire, the actress, 28, gets candid about all the challenges with the many, many sex scenes she shared with costar Jamie Dornan.

Strapless Thongs And Superglue

The chemistry between the two costars may be palpable onscreen, but Johnson says sex scenes never became easy or less awkward at any point in the three films. It's not surprising given the nature of the pair's ultra-intimate scenes. Plus, even their underwear is far from comfortable.

While her costar Jamie Dornan had what she called a "little pouch," Johnson reveals that she also had to wear special strapless thongs to protect her modesty while filming.

"It would also come off because the adhesive would wear out, so then they would superglue it to my body so that it wouldn't fall off," she recalls. "And I would wear two of them. It's not painful, I mean, it's barely anything."

At least, she adds, there's the illusion that parts of her body are being concealed.

"It's f--king bizarre," Johnson concludes.

Most Difficult Scene Of The Franchise

With the source material, it is expected that Johnson will have to endure plenty of out-of-the-box intimate scenes. The entire team behind the Fifty Shades franchise were prepared for it with sex scene shooting schedules, BDSM expert advisors, and even shots beforehand if the scene is particularly challenging.

There are many scenes to choose from over three full-length films, but when asked what the toughest one was, the actress didn't hesitate to respond: the Red Room. Handcuffed and blindfolded, even Johnson did not anticipate the challenges involved in shooting the infamous scene.

"And it was kind of shocking, because I didn't realize that no matter how prepared or rehearsed I was, when your senses are taken away like that, you can't control the way your nervous system will react," she explains. "So it was really tricky to navigate that scene."

Saying Goodbye To Christian, Anastasia

Now that the last film of the trilogy has wrapped, Dornan and Johnson are ready to say goodbye to their iconic characters.

In an interview with Entertainment Tonight, Dornan calls the end of the film series "bittersweet," adding that it's nice to move on from the project that took them over four years to complete.

Johnson agrees, saying the trilogy gave her something to be proud of, and she's looking forward to her career post-Fifty Shades.

Next up for the actress is adventure movie The Peanut Butter Falcon with Jon Bernthal (The Punisher) and Shia LaBeouf (Transformers). It's slated to be out within the year.

Meanwhile, Dornan will star in A Private War with Rosamund Pike and Stanley Tucci.

Fifty Shades Freed is now in theaters.

Tags: Fifty Shades Freed dakota johnson jamie dornan