Blackstone Inc. /zigman2/quotes/203156858/composite BX -2.98% said Wednesday it has agreed to acquire a majority stake in Spanx Inc., the womenswear brand founded by Sara Blakely in 2000, in a deal that values the brand at $1.2 billion. Blakely will retain a "significant equity stake" in the company, and will continue to oversee daily operations and become executive chairwoman once the deal closes. The deal "will enable SPANX to accelerate its already rapid digital transformation and strong online presence in the e-commerce channel, expand its global footprint, and fuel its commitment to creating innovative, ground-breaking products for its customers across even more categories," the companies said in a joint statement. The companies are planning to create an all-female board for the company. Blakely started the company by inventing the first Spanx undergarment in her own apartment, at a time when she was earning a living selling fax machines door to door. Blackstone shares were slightly higher Wednesday and have gained 96% in the year to date, while the S&P 500 /zigman2/quotes/210599714/realtime SPX -2.27% has gained 21%.