Kate Gosselin “commanded” her eight children to “act happy” as young children, or they would face her wrath, her son Collin Gosselin claims.

In his new memoir, “In the Shadow of Eight: Surviving the Reality of My Childhood,” which hit bookshelves Tuesday, Collin alleges his now-estranged mom forced her eight children to act a certain way in front of cameras while the family filmed their hit TLC show, “Jon and Kate Plus 8.”

“For us kids, the script was nonnegotiable: behave, act happy, smile. If any of us slipped and became overwhelmed (and showed it), she’d lean in and hiss through clenched teeth: ‘Smile,’” he writes.

Kate Gosselin (pictured with her eight children in 2012) would allegedly punish her kids if they didn’t “act happy.” Disney General Entertainment Content via Getty Images

Collin Gosselin (pictured far left with his siblings as a child) exposes his mom’s alleged strict rules and consequences in his new memoir. Disney General Entertainment Content via Getty Images

Collin, who was just a year old when their show started filming, recalls he and his siblings being punished for behavior considered normal for young toddlers.

After one incident, where he hit his brother Aaden in the head while fighting over a toy, Kate allegedly sent him to her version of timeout, which was sitting in the corner with his nose pressed against the wall while the rest of his family was “supposed to pretend [he wasn’t] there.”

Another of Kate’s alleged “unreasonable expectations” for her little ones was that they were not allowed to get any stains on their clothes.

“If we got even the littlest bit of dirt on our clothes, we’d be stripped down and punished,” Collin claims.

“If any of us slipped and became overwhelmed (and showed it), she’d lean in and hiss through clenched teeth: ‘Smile,’” Collin (pictured last month) writes. Getty Images

According to Collin, his mom’s version of timeout was making the kids sit with their nose pressed against the wall while the rest of the children pretended they weren’t there. Getty Images

Other rules Collin recalls under Kate’s supervision included being allowed to use only a “tiny dot” of shampoo while showering and getting in trouble if it got under their fingernails.

Additionally, “deodorant was one swipe up, one swipe down.”

According to Collin, his mom’s harsh energy was noticed by all of the show’s production members, who would “just go quiet around her,” even those who had authority.

The 22-year-old recalls Kate being “particularly hard” on him, often picking on how he smiled or how he acted.

The kids would also allegedly be “stripped down and punished” if Kate (pictured with Collin as a baby) saw a stain on their clothes. MediaNews Group via Getty Images

The children (pictured in 2012) were also only allowed to use a “tiny” dot” of shampoo, per Collin. Disney General Entertainment Content via Getty Images

Also in the memoir, Collin recalls an alleged screaming match between his dad, Jon Gosselin, and his mom while the TLC cameras were down. During the fight, Collin writes that he and his siblings cowered behind one of the doorframes in the house.

“Just raw anger, bouncing off every surface of that house, exploding in our ears.”

Jon lost custody of all eight of his children when he and Kate divorced in 2009. The show was then rebranded to “Kate Plus 8,” which ran from 2007 to 2017.

Collin has been estranged from his mother since 2016, when she sent him to live in a behavioral health institution at 11 years old for allegedly being violent and exhibiting unpredictable behavior.

Collin and Kate have been estranged since 2016, when she sent him to a behavioral health institution. Three years later, his father, Jon Gosselin (seen above, along with Collin and sister Hannah) got him out and got custody of him. jongosselin1/Instagram

Jon also got custody of Hannah (pictured here), one of Collin’s sextuplet siblings. jongosselin1/Instagram

Three years later, Collin reunited with his father, who got him out of the facility and granted legal and physical custody.

Jon also got custody of Hannah Gosselin, one of Collin’s sextuplet siblings, after she left Kate’s house.

The rest of the sextuplets — Joel, Alexis, Leah, and Aaden — continued living with Kate, along with their older twin sisters, Mady and Cara, 25. They continue to remain estranged from Jon and Collin.

As Page Six previously reported, Collin announced the bombshell memoir in June and promised to expose “the shocking facade of his picture-perfect family.”

The rest of the sextuplets continued living with Kate along with their older twin sisters (all seen above). kateplusmy8/Instagram

Collin has accused his mom (pictured in 2019) of abuse for years, though she has vehemently denied it. Getty Images

After her son’s announcement and ongoing accusations of abuse against her, Kate called Collin “mentally ill” and claimed she is being “constantly disparaged and lied about” by an “adult child with a skewed version of their childhood.”

Despite vehemently denying all of her son’s claims, Page Six exclusively reported last month that the “Dancing With the Stars” alum is “nervous” about the book’s release.

“There is no doubt Kate is nervous this book is about to hit,” a source told us. “Kate doesn’t want anyone in the family to talk about their past. She considers any of the children who talk in the family as traitors.”

After Collin (seen above) announced the tell-all, Kate called him “mentally ill.” JISH / BACKGRID

Last month, Page Six exclusively reported that the matriarch (pictured in June) is “nervous” for her son’s memoir to come out. Christopher Oquendo for NY Post

As for Collin, he isn’t concerned with what his mom thinks of him or his book.

The reality TV star, who recently competed on Season 5 of FOX’s “Special Forces: World’s Toughest Test,” had a savage message for Kate when Page Six asked him if he had anything to say to her in case she tunes in.

“Well, if she does, ‘Hey, Mom!’” Collin, 22, said with a laugh at the “Special Forces” red carpet event in Los Angeles last month. “Hope you enjoy.”