Katie Couric will guest-host on 'Good Morning America' Katie Couric is returning to morning TV, for a week anyway. But what's got people raising their eyebrows is where she's doing it -- ABC's "Good Morning America." Couric, who has a deal with Disney-ABC Domestic Television for a daytime talk show called "Katie," which will debut in September, will be filling in for regular GMA co-host Robin Roberts, who is off on vacation next week. Roberts made the official announcement Thursday morning and Couric tweeted, "Rise + shine! Excited to be back on morning TV next wk, guest hosting @GMA w/ @GStephanopoulos. #KatieOnGMA. The news can't be welcome over at Couric's old home at NBC. While "Today" is still the No. 1-ranked morning show, "GMA" is on the rise. According to the average ratings for the week of March 12, "Today" was just 260,000 viewers ahead of "GMA," the smallest gap between the two since July 2008. Couric made her name on "Today," where she began as a national correspondent in 1989. She soon became the permanent co-anchor in 1991 when Deborah Norville didn't return to the show. In 2006, she left "Today" to become the anchor of the "CBS Evening News," where she stayed for nearly five years. Katie Couric will be 'all over the place,' ABC News boss says Photo: Katie Couric. Credit: Jamie McCarthy / Getty Images