The prospective first lady will help host the show during the 8 a.m. hour on Oct. 10.

It will be one of the most high-profile media appearances yet for Romney, who in September stepped into the national spotlight with her speech at the Republican National Convention. She has since appeared on "The Tonight Show" and "Access Hollywood," broadening her media exposure beyond morning news shows such as "Fox and Friends."

ABC also wants to book first lady Michelle ObamaMichelle LeVaughn Robinson ObamaObama plans to use Netflix deal to stop political divisiveness Michelle Obama tweets out first look at cover of new book Netflix surpasses Comcast in market value MORE as a guest host, and the first lady has reportedly expressed interest. It would be a natural fit for Obama, who has often appeared on daytime talk shows.

The show's usual co-anchor, Robin Roberts, is on medical leave. Roberts left "Good Morning America" at the end of August to undergo a bone marrow transplant.

Other planned guest hosts include Stephen Colbert, Oprah Winfrey, Katie Couric, Rob Lowe, Barbara Walters and Diane Sawyer.

Updated at 3:33 p.m.