Learning about their father's affair with housekeeper Mildred Baena is bad enough. But psychologist Andrew Yellen says having to deal with a sibling kept secret from them for 13 or 14 years takes the betrayal to another level.
"You have somebody that's in the home and this lie is being lived out every single day in front of Ms. Shriver and the other four children," Yellen said. "To find out about that afterwards, it kind of shakes your world right down to the core."
Yellen says it's a life-changing ordeal that more often than not will require long-term counseling.
"Going down the line, there's always in the back of somebody's head, is this going to happen to me? Can I trust the person I'm with? Can that person trust me? And we go back to bringing up a post-traumatic stress type of thing," Yellen said.
The lie will affect Schwarzenegger's son with Baena as well. Yellen said he believes the boy may become the scapegoat everyone blames, unjustly so.
"He's going to get called names, and he's going to get made fun of," Yellen said. "Here he is as somebody's love child, as opposed to having a father, mother and normal situation, so his life as he knows it is no longer."
Yellen says Shriver's children can recover from this blow if they get the proper help and receive the right queues from their mother.
"You are your child's best role model," Yellen said.
Schwarzenegger's older children have tweeted about the situation this week.
Their son Patrick Schwarzenegger tweeted, "Some days you want to quit and just be normal for a bit, yet I love my family, till death do us apart," referencing a popular song by Fort Minor. The song is about the consequences of choosing a career over family.
The couple's oldest daughter Katherine also tweeted, "This is definitely not easy but I appreciate your love and support as I begin to heal and move forward in life.I will always love my family!"
Some experts might find the medium inappropriate, but Yellen says Twitter and Facebook are being used by many young people now to address and deal with serious matters.