Viewers of Jon & Kate Plus 8 have long known that the oversize family’s matriarch was tough. But startling new accusations against Kate Gosselin by one of her 20-year-old sextuplets, son Collin, go beyond the tough-love norms. In a shocking new interview, Collin, who has previously called out his mother for her harsh treatment of him, alleges that he was tied up and locked into a “containment room” in the family’s basement starting before he turned 10. “I was there, you know, most of the day because I didn’t go to school after a point,” he told a news source, adding that Kate “zip-tied my hands and feet together and bolt locked the door, turned the lights off and had cameras there just watching me.”

Earlier, Collin spoke out about being institutionalized by the 49-year-old, who alleged he was violent. (Kate’s attorney said she “did what she did to protect herself and her family” from his alleged “troubled behavior.”) “Kate makes no apologies for her treatment of Collin,” an insider exclusively tells In Touch. “Of course, when Collin tells it, it sounds like a horror story.”

Indeed, the day after his interview, Collin took to Instagram, writing September 10, “It has taken me a long time to find the strength needed to speak about my mother’s abuse,” adding, “I hope to be the voice for children everywhere facing abuse.” He also thanked his father, Jon Gosselin, who split from Kate in 2009, for fighting for custody of him and sister Hannah, 20. (The 47-year- old is estranged from his other kids.) He said, “Today I feel a small sense of justice by speaking [up].”