Oprah Winfrey and Reese Witherspoon join in a private equity takeover of Spanx.

Oprah Winfrey, Reese Witherspoon and the Bumble founder Whitney Wolfe Herd are joining Blackstone in investing in Spanx, the DealBook newsletter was first to report. Blackstone closed its deal to acquire a majority stake in the shapewear brand that values it at $1.2 billion on Thursday.

Founded more than 20 years ago, Spanx has become synonymous with the foundation garments it sells. Ms. Winfrey helped put the brand on the map in its early days when in 2000 she named Spanx her favorite product of the year. (Sara Blakely, Spanx’s founder, said that Ms. Winfrey had earlier validated her business idea when the talk show host told the audience one day that she cut the feet off her pantyhose.)

“I’m happy to be part of the evolution,” Ms. Winfrey said about the brand in a statement.

It’s the latest investment deal for Ms. Winfrey and Ms. Witherspoon, whose financial backing is valued as a stamp of approval for consumer brands. The TV and film stars are also familiar partners for Blackstone. Ms. Winfrey invested alongside Blackstone in Oatly, the oat milk brand that went public earlier this year. Blackstone also recently acquired Ms. Witherspoon’s Hello Sunshine production studio, adding her to the board of its parent media company. Wolfe Herd’s Bumble, a dating app, was acquired by Blackstone in 2019 before going public earlier this year.

Ms. Winfrey, Ms. Witherspoon and Ms. Wolfe Herd are investing in Spanx directly, outside of any Blackstone fund. They were also joined by the investment funds G9 Ventures and Able Partners.

Blackstone and Spanx had previously said that they intended to create a board comprising solely women. Ms. Blakely, who put the company up for sale earlier this year without ever having taken on outside investment, is keeping a significant equity stake in the business.

“In addition to developing a remarkable product and business that literally supports women every day, Sara has become a role model for leveraging your success to elevate other women,” Ms. Witherspoon said in a statement.