EXCLUSIVE: Mama June, Now a Size 4, Enjoys Walking Around the House in 'Her Underwear,' Says Daughter Pumpkin

ET chatted with the reality star's daughters and fitness trainer ahead of her new docu-dramedy, 'Mama June: From Not to Hot,' airing Friday on WE tv.

Mama June is loving her slimmer figure!

Ahead of her new show, Mama June: From Not to Hot, which premieres Friday on WE tv, ET caught up with the 37-year-old reality star's trainer on the docu-dramedy, Kenya Crooks, who opened up about his client's dramatic physical transformation.

WATCH: Mama June's Weight Loss Surgeries Revealed -- How She Went From 460 Pounds to a Size 4

According to the fitness trainer, the former Here Comes Honey Boo Boo star has been doing a lot of strength training, crunches, plyometrics and running after undergoing multiple weight-loss surgeries.

"The cool thing is, you get to see her transformation not only from a physical standpoint, but you also get to see her change here, you know, from a mental standpoint," Kenya explained to ET's Jennifer Peros on Wednesday. "Because at first, I don't want to tell too much about the show, but at first, she was doing it for different reasons, but, as you will see throughout the episodes, it's more about her now."

ET also caught up with Mama June's daughters, 17-year-old Lauryn "Pumpkin" Thompson and 11-year-old Alana "Honey Boo Boo" Thompson, who revealed their mother is happier than ever -- and much more confident!

"I ain't trying to be like R-rated or anything, but she walks around the house in a pair of her underwear now, so...," Pumpkin joked. "Uh huh. I'm like, 'June, put some pants on! Put some pants on!'"

WATCH: Mama June Documents Extensive Plastic Surgery, Body Transformation in New Show 'From Not to Hot'

Pumpkin told ET that despite Mama June's total body transformation, there's still some days when she sees the old version of herself.

"Momma's doing really good," Pumpkin said. "I think that her biggest [insecurity] that she still has to [get over] is that fact of, I think she still thinks of herself as a bigger person. Because, even to this day, like a couple of days ago, we had a conversation, and she is like... she looked in the mirror and was like, 'I'm still fat.' And I guess because she's seen herself as a bigger person all these years, she doesn't realize how small she is."

"She tries to wear bigger clothes and baggier clothes and stuff like that, and we're like, 'You're small, like wear something, you know, tight-fitting,'" she added.

That may explain why her wardrobe still consists of loose-fitting clothes.

"She doesn't want to [buy new clothes]," Pumpkin revealed.

WATCH: Mama June Drops Down to a Size 4 After Weighing 352 Pounds

Kenya chimed in, telling ET, "That's what she's used to doing."

"When you're a bigger person, that's how you disguise all of that, through wearing bigger clothes," he dished. "So now, we're having to transform her mind even more, because she has curves now, she looks awesome."

And while Mama June clearly looks different on the outside -- which fans will get to see during the finale of the seven-part series! -- Pumpkin and Honey Boo say she's still the same, "just smaller."

"I'm really happy for her because I think she's always seen herself as a small person," Pumpkin exclaimed. "Even though now she's having a hard time realizing that she is a small person, I think that she's always, within that big person, that she's always been, she's always seen the smaller person."

"[Hugging her is] so different," said Honey Boo Boo, adding that her mom is kind of crazy about getting on the scale every day. "I can wrap both my arms around her."

WATCH: Mama June Says Sugar Bear Cheated on Her With Men and Women

"I kind of didn't want her to do it at first," she continued, "but after she [did] it, I'm very happy with it and how she turned out."

Kenya also told ET that he's been lecturing Mama June on the importance of keeping up with her diet and fitness routine in order to maintain her trimmed-down figure. Luckily, her daughters have been keeping her in check.

"Most of the time I'm up late at night anyways, but I tell her like, 'Momma, you can't do that,'" Pumpkin said about monitoring her mom's late-night snacking habit. "I have to show her [old] pictures of her sometimes, and she's like, 'I can't even believe that's me.' I'm like, 'If you don't stop eating that junk, you're going to go right back!'"

WATCH: Inside Mama June's Diet and Exercise Plan That Led to Her Stunning Weight Loss