Cynthia Bailey's sister returns to The Real Housewives of Atlanta this season -- and she has a big announcement that could hurt Cynthia and her husband Peter Thomas’ relationship.

In a new preview for Sunday night’s episode, Malorie Bailey-Massie drops a major bombshell: she’s relocating to Atlanta for a few months — and is moving into the couple’s home.

Peter protests the move.

“You just move into people’s houses without asking them?” Peter questions, before turning to his wife. “We never had a talk about this at all... I’m surprised.”

“I didn’t know. She just told me,” Cynthia tells Peter.

“Surprise!” Malorie smirks.

As RHOA fans may recall, Malorie and Peter have never gotten along: She tried to hide the couple’s marriage license on their wedding day and revealed during filming that she was concerned that Peter was taking advantage of her sister and her finances.

“These types of things need to be between you and I,” Peter tells Cynthia.

Cynthia explains to the Bravo cameras, “My family is always