Jennette McCurdy shared why she was "jealous" of Ariana Grande while being a Nickelodeon star. 

In her new memoir, "I’m Glad My Mom Died," McCurdy, 30, got candid about her "Sam & Cat" co-star. McCurdy referred to Grande as a "burgeoning pop star" who "regularly" missed filming.

According to McCurdy, Grande was absent "to go sing at award shows, record new songs, and do press for her upcoming album," while she was left to "angrily hold down the fort."

"Sam & Cat" aired for only one season during 2013-2014, and after the show's cancellation, Nickelodeon offered the former actress $300,000 to keep her experiences at the network private, McCurdy said. She refused the offer.

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McCurdy, who played Sam Puckett on "iCarly," sympathized with Grande but was still upset because she was not given the same opportunities, according to the star.

"I booked two features during ‘iCarly’ that I had to turn down because the ‘iCarly’ team wouldn’t write me out of episodes to go shoot them," she said.

At first, Grande’s absences were sporadic but eventually, the actress and singer reportedly missed an entire week on set.

"The week where I was told Ariana would not be here at all, and that they would write around her absence this episode by having her character be locked in a box. Are you. Kidding me," McCurdy wrote. "So I have to turn down movies while Ariana’s off whistle-toning at the Billboard Music Awards? F**k. This." 

The situation led McCurdy to "resent being a good sport," which she was often praised for in the past.

"If I wasn’t such a good sport to begin with, I wouldn’t be in this predicament in the first place. I wouldn’t be on this sh**ty show saying these sh**ty lines on this sh**ty set with this sh**ty hairstyle," she wrote. 

"Maybe my life would be entirely different right now. I fantasize about it being different. But it’s not different. It’s this. This is what it is. Ariana misses work in pursuit of her music career while I act with a box. I’m pissed about it. And I’m pissed at her. Jealous of her."

McCurdy noted that her jealousy came from the fact that she believed Grande had a "much easier upbringing."

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"I grew up in Garbage Grove in a god**mned hoarder house with a cancerous mom who constantly wept about not being able to afford rent and utility bills," she wrote in her memoir. "Ariana grew up in Boca Raton, Florida, an incredibly wealthy, idyllic town, with a healthy mom who could buy her whatever she wanted, whenever she wanted -- Gucci bags, fancy vacations, Chanel outfits."

McCurdy wrote that she was initially approached for her own show on Nickelodeon and resented starring alongside Grande.

"When I initially got a development deal with Nickelodeon for my own show a few years ago, I thought it was gonna be just that... my own show," she wrote. "This was supposed to be ‘Just Puckett,’ the harrowing tale of a brassy juvenile delinquent-turned-school counselor. Now it’s some half-baked two-hander -- ‘Sam & Cat’ – about a brassy juvenile delinquent who, with her 'ditzy best friend,' starts a babysitting company called 'Sam & Cat’s Super Rockin’ Fun-Time Babysitting Service.' This is not harrowing."

She also credits her jealousy to that fact that Grande’s career flourished while she views her own as stagnant.

"Ariana is at the stage in her career where she’s popping up on every 30 Under 30 list that exists. And I’m at the stage in my career where my team is excited that I’m the new face of Rebecca Bonbon, a tween clothing line featuring a cat with her tongue sticking out. Sold exclusively at Walmart," McCurdy wrote. 

"And I frequently make the mistake of comparing my career to Ariana’s. I can’t help it. I’m constantly in the same environment as her, and she doesn’t exactly try to hide her successes."

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McCurdy says she felt undermined by the network as they discouraged her from exploring other career opportunities outside the show. However, those rules did not seem to apply to Grande. 

"What finally undid me was when Ariana came whistle-toning in with excitement because she had spent the previous evening playing charades at Tom Hanks’s house. That was the moment I broke," McCurdy wrote.

This is not the first time McCurdy has addressed her feud with Grande. In 2017, McCurdy told E! News that the duo had a "sisterly" relationship and claimed there was no bad-blood between the stars.

"Some [people] like drama and I think we butted heads at times but in a very sisterly way. She knows me so well and I know her so well that I think it was unfortunate that things kind of got misconstrued," she said at the time.

McCurdy’s memoir, which details her toxic relationship with her mother and her tumultuous time on Nickelodeon, was released on Tuesday. She recounted auditioning for acting roles at the age of 6 and being "shepherded" into the work by her controlling mother. 

McCurdy also noted that she suffered from obsessive-compulsive disorder, eating disorders and anxiety. The actress believed she owed her loyalty to her mother, who controlled every aspect of her life. 

Fox News' Stephanie Giang-Paunon contributed to this report.