What is the episode when Phineas and ferb find out there mother is a popstar?

Season 2, Episode 35 b - 'Ladies and Gentlemen: Meet Max Modem' is the episode in which Candace finds out that their mother is a popstar, but in the very same episode Phineas and Ferb tend to say that they knew this from before, so there is no particular episode in which they show that Phineas and Ferb realize that their mother is a popstar.