In late August, Kate Gosselin revealed that her son, Collin, is away getting help for emotional and behavioral issues.
The news surprised Kate Plus Eight fans, but Gosselin herself had been struggling with the 12-year-old's problems for years.
Gosselin wrote a letter to her son, which was published in her 2010 book, I Just Want You To Know.
In the excerpt, obtained by Radar Online, Gosselin praised her son's sweet nature and strong mathematical skills, but those traits were overshadowed by his attitude.
"As you have grown, however, I must say you have also challenged my authority greatly,” Gosselin admitted.
“At two and a half, you began testing and trying my parenting at every chance. I called Daddy at work many days crying because you would not obey.”
"As you have grown, this fact has not changed. You continue to be determined to do what you want to do, and I continue to try to rein you in."
Gosselin brought up her frustration with Collin several times in the past, but viewers had no idea it was so extreme.
“I know the recent events in our family structure have greatly upset you, maybe you most of all,” Gosselin wrote, referring to her divorce from Jon Gosselin.
“I want you to know that I have made and will continue to make decisions based on what I believe is best for you and your brothers and sisters.
These changes, I realize, are still painful and hurt a lot.”
Gosselin ended the letter by assuring her son, who is one of sixtuplets, that he would always have a special place in her heart.
"Collin has special needs," Gosselin explained to People Magazine in a feature interview.
"[There's] a fairly fluid diagnosis of what those needs are, but he needs to learn certain strategies to help him deal with things.
"This has been a struggle we've had for a very long time, and it's one I've dealt with on my own.
"I've felt very alone in this. By the same token, it's not something that has only impacted me or him – our entire family has been impacted."
Collin is "enrolled in a program that is helping him learn the skills he needs to be the best him he can be," the reality star added.
"We miss him so much, so it's been hard because there is a huge hole in our family without him here.
"But it comforts us to know he's where he needs to be right now, and I can feel good about that."
Both Collin and his sister, Alexis were removed from their school in 2010 for failing to obey the rules.
Both kids were homeschooled thereafter, and Gosselin took great pains to stress that they had not been "expelled."
The school, Gosselin said, "would never use that word."
Instead, Gosselin explained, both she and the school agreed that the kids' meets could be better met with one-on-one tutoring.
It is not known when Collin will return home to his family.