WENN
Earlier this week, reports claimed that Jonas would appear in the programme as a young Tommy Walker, played by Balthazar Getty.
However, Entertainment Weekly reports that Jonas will not be joining the show because of a "scheduling conflict".
Cody Longo, who stars in Make It Or Break It, is now expected to take on the role in the two-hour flashback episode.
Executive producer David Marshall Grant said that the episode will be set in three different time periods and added that it will expose a "shocking and transformative" secret about the Walkers.
Brothers & Sisters continues on Sundays at 10pm on ABC in the US and Thursdays at 10pm on More4 in the UK.
