Bristol Palin, daughter of former GOP vice presidential candidate Sarah Palin, is apparently joining the cast of "Teen Mom: OG." Earlier this morning, Palin confirmed the news on her Instagram account: Per TMZ, Bristol, 27, "signed on as a regular on the show," and is set to debut this fall alongside Amber Portwood, Catelynn Baltierra and Maci Bookout. Longtime "Teen Mom" insider Ashley Majeski, of "Ashley's Reality Roundups," has since confirmed the report, adding that Bristol has been shooting for the show "for a few weeks," but under a cloak of secrecy:"Amber, Catelynn and Maci did not even know... It was kept under wraps because MTV was afraid that Sarah would pull out, and MTV knew that the original girls would be upset. In fact, they even used a different name when discussing Bristol being on the show, to keep it a secret!"TMZ is reporting that another new mom would also be joining the OG mix — Mackenzie McKee, formerly of "Teen Mom 3." (McKee's casting has been widely speculated in recent months.) Majeski, however, says that's not true, and that the fifth spot is instead being taken by Cheyenne Floyd, formerly of MTV's dating show "Are You The One?"Cosmopolitan.com reached out to MTV for comment, but did not receive a response. As pictured above in a photo from her Instagram, Bristol has three children — a son, Tripp, with former fiancé Levi Johnston, and two daughters, Sailor and Atlee, with husband, former Marine Dakota Meyer. In February Meyer filed for divorce, though recent reports and posts of them together on Instagram, suggest the couple have since reconciled. Bristol's first pregnancy was infamously announced at the 2008 Republican National Convention, along with her engagement to Johnston — she was, at the time, 17 years old. Tripp was born a month after the 2008 presidential election; she and Johnston ended their engagement in March 2009.Her previous reality TV credits include two stints on "Dancing With The Stars," and her 2012 Lifetime docu-series "Bristol Palin: Life's a Tripp."