Joe Jonas, Cody Longo

Brothers & Sisters has locked in three guest stars for an upcoming flashback episode that shows the Walker siblings as teenagers, TVGuide.com has confirmed.

Check out photos of the Brothers & Sisters cast

Early reports had tween heartthrob Joe Jonas playing a young Tommy Walker (Balthazar Getty), but a scheduling conflict forced him to back out. Taking his place will be Make It or Break It's Cody Longo.

Kay Panabaker (Fame) will play young Kitty (Calista Flockhart), newcomer Anna Wood (Royal Pains) will play the eldest sibling, Sarah (Rachel Griffiths) and Kasey Campbell is in negotiations to play Kevin (Matthew Rhys). It's unclear if Justin (Dave Annable) will appear in the flashbacks, according to E! Online. The episode will also portray a younger William and Nora Walker, as well as William's mistress, Holly Harper. Those roles remain uncast.

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"[The flashbacks] are all in service of understating secrets of the past that are slowly revealing themselves now," executive producer David Marshall Grant tells TVGuide.com, noting that the two-hour episode kicks off a series of episodes that really test the Walker family.

The flashback-heavy episode airs April 11 at 9/8c on ABC.