Ashlee Simpson has recalled the "insane" bullying she experienced after her lip-sync fail on Saturday Night Live.

The 40-year-old was discussing the highs and lows of her career during an appearance on the Pod Meets World podcast on Thursday. Co-host Danielle Fishel asked Ashlee about the incident, which took place in 2004 and saw the singer become the first musician to walk out of an SNL performance.

Ashlee, who was 20 at the time, was left floundering after her hit single Pieces of Me began to play along with her pre-recorded vocals before she had even raised a microphone to her mouth.

"I think it's a different era ... I think during that time, I mean, the bullying was insane," the 40-year-old star insisted.

Ashlee had been expecting to perform her song Autobiography and was caught on camera looking confused, before she danced erratically and left the stage as her band continued to play. The decision to lip-sync sparked a huge backlash against the singer, who later explained an acid reflux flare-up had affected her voice.

During the interview on Thursday, Ashlee admitted she has spent years trying to make up for the unfortunate incident.

She continued, "But then my whole life, I had to tell people, 'Oh, but I perform every night.' My fans know. I had to know that in my heart."

"Yes, I've had ups and downs just like every other human," she admitted.

Ashlee continued to discuss the tougher moments of her life as she recalled the release of her debut album Autobiography in 2004.

Referring to the record as the "diary of my life", the star revealed a toxic relationship inspired some of her lyrics.

"I had a boyfriend that was like, 'You look fat, you need to get on the treadmill!'" Ashlee shared, before she laughed and added her first thought was, "Get ready for what I'm about to say."