EXCLUSIVE: Kardashian family is 'mortified' by Rob's social media outburst, concerned about Dream, source says

The Kardashian family may be staying silent on Rob Kardashian's social media outburst on Wednesday, but they definitely have an opinion.

A source close to the family tells ET that they are "mortified" over Rob's behavior, but are mostly concerned for his and Blac Chyna's 7-month-old daughter, Dream.

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"What happened was so low and inappropriate. It's very frustrating to deal with a person who can't control himself," the source says. "His family and close friends asked him to stop posting yesterday, but he wouldn't listen. He won't listen to anyone. The family can only do or say so much."

The most embarrassed of the family is Rob's mom, Kris Jenner, the source says.

See photos of Rob and Chyna together:

"Kris never publicly defamed Cailtyn in their relationship or what happened after. She never said one unpleasant thing about Caitlyn in the media. Kris handled that situation with class, and she was hoping Rob would follow that example," ET's source reveals. "Kris has done so much for Rob, but no one knows what else they can do for him anymore."

The source says Rob was alone in his own home in the Calabasas, California, area when he took to Instagram and Twitter on Wednesday, accusing Chyna of cheating on him multiple times. The 30-year-old reality star also shared several nude photos allegedly of his ex-fiancee, and claimed to have been paying for her rent, cars and $100,000 worth of surgery after she gave birth to Dream.

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According to ET's source, Dream is the family's No. 1 priority.

See photos of Kris Jenner:

"Everyone's main concern is Dream. At the end of the day, Chyna is Dream's mother, and she will always be in the picture, so it doesn't matter what Rob thinks of her or what she's done to him," the source says. "The comments, pictures and videos he posted yesterday will live on the internet forever, [and] one day, Dream will see what her dad said and did to her mother."

Despite Rob's claims that Chyna was unfaithful, a source tells ET that the two "haven't been together in a really long time."

"Chyna has been keeping him to the side for a long time. Whenever she needs something, she'll call Rob, and unfortunately, he keeps sticking around hoping that they can get back to the good spot they once were in. He won't realize that what they had will never be there again," the source reveals. "Chyna will also never change. Chyna needs Rob for many things -- mainly financial. But no matter what Chyna ever did to Rob, this is about Rob being a responsible person and a good father."

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The Kardashian family is still grateful for the good things Chyna did for Rob, however. "Chyna was responsible for him getting out of his depression and changing his life," the source explains. "Before her, he was in such a bad place."

Reporting by Jennifer Peros.

Wednesday's outburt isn't the first time Rob and Chyna have made headlines throughout their relationship. Relive their most dramatic moments in the video below.