He knew who she was before she joined Cody Banks 2, even though S Club aren't nearly as famous in the US as they are in the UK.
Frankie also said he was about to start filming the fifth series of Malcolm in the Middle.
Hannah's not the only S Club member to be starting a new career.
Rachel's signed a £1 million solo deal, and John will have his debut in the West End musical Les Miserables on Monday 28 July.
Hannah said all the other old S Clubbers were going to support him on his first night.