As Celine Dion showed exactly how the she has affects her singing voice, she broke down in tears.

“It’s very difficult for me to show this to you,” Dion, 56, said as she breaks the fourth wall in her groundbreaking documentary, I Am: Celine Dion.

Directed by Academy Award nominee Irene Taylor, the feature-length film will give fans of the singer rare access into her life after she was diagnosed with the extremely rare (SPS).

It affects only one or two people in every million and is a progressive autoimmune neurological disorder which causes muscle stiffness and pain spasms, and usually begins in a person’s torso before developing in the arms and legs.

“Before I got really hit with SPS, my voice was the conductor of my life. I was following it,” she said in the clip from movie.

“‘You lead the way and I’ll follow you.’ And I was OK with that because I was having a great time. When your voice brings you joy, you’re the best of yourself.”

Dion says of her voice, “‘You can be the leader, my ego is not that big. If you want to take it I don’t care. I’m having a good time here.'”

With that explanation of how important her voice was to her, Dion then described the physical pain of the disease.

“Sometimes when I try to breathe my lungs are fine. But it’s what is in front of my lungs that is so rigid,” she said, as she tried to sing but struggled to hit notes or project her voice.

“There’s been moments I had to go to the studio and I know they wanted Celine Dion?” the singer said of the expectations she faces of trying to still deliver her iconic voice.

She adds: “But who’s Celine Dion? She sang to the highest note ever. She’s the best.”

The singer also reflected on her talents while in tears: “I think I was very good. I think I had some stuff that was amazing.”

The documentary premieres on Prime Video on June 25 and flies through Dion’s most remarkable successes and personal life to focus on her battle to get back on to the stage.

One confronting scene even shows Dion going into “crisis,” where her foot stiffened and then suddenly her entire body went rigid. Her health team were on the precipice of calling 911 until the meds they’d given her kicked in.

Dion explained how she barely left her Las Vegas home anymore and wanted to make the documentary because she’d always been an “open book” with her fans and no longer wanted “to lie to you.”

The Quebec-born singer is one of the most successful music artists of all time and has sold more than 250 million albums worldwide.

Her number-one hits include “The Power of Love,” “It’s All Coming Back to Me Now,” “My Heart Will Go On,” and “Because You Loved Me.”

She has won five Grammy Awards, two Academy Awards, seven American Music Awards and an incredible 43 Félix Awards—Quebec’s music awards

In 2004, the World Music Awards gave her diamond status as the best selling female artist of all time and in 2016 the Billboard Music Awards presented her with the Lifetime Achievement Icon Award.

If that wasn’t enough, her Las Vegas residencies remain the two highest-grossing of all time.

Two years ago she revealed her condition was causing muscle spasms that impacted her ability to sing and walk.

“While we’re still learning about this rare condition, we now know this is what’s been causing all of the spasms that I’ve been having,” she said in a video posted to . “Unfortunately, the spasms affect every aspect of my daily life, sometimes causing difficulties when I walk and not allowing me to use my vocal cords to sing the way I’m used to.”

I Am: Celine Dion will be available on Prime Video on 25 June.