Collin Gosselin fully believes his side of the story about mom Kate Gosselin's alleged affair. "This is my formal invitation to do a lie detector test with my mom lol," Collin, 21, wrote via his Instagram Story on Thursday, September 25. "Then, we'll see who's been lying straight to the public. I'm so serious by the way." Collin and his father, Jon Gosselin, previously claimed that Kate's rumored new boyfriend is Steve Neild, the family's former security guard with whom she allegedly had an affair. (Kate, 50, has not addressed the accusations. Us Weekly reached out for comment.