Miley Cyrus should be watching out her back as Maria Shriver, her boyfriend's [Patrick Schwarzenegger] mother, has threatened to end their relationship, a source close to the couple revealed. It seemed that Cyrus is still not accepted by the Kennedys and Shriver is really trying hard to knock some sense to her son about the relationship.

"[Maria Shriver] is hoping that he will come to his senses and realize that Miley does not fit in his world," the Hollywood Life source said.

Miley Cyrus and Maria Shriver had been at odds when the latter did not approve the relationship of her son with the pop star. And recently, Hollywood Life reported that Cyrus was banned from a family birthday party for Schwarzenegger's sister. The source revealed that the "Wrecking Ball" singer was not invited and still not welcomed by her boyfriend's family.

"Patrick is very close to his sister he's not going to go against what she asks, especially not on her birthday," our source explained.

However, it seemed that the rift between Miley Cyrus and Maria Shriver has also dragged Patrick Schwarzenegger into the scene. The Daily Mail reported the mother-and-son relationship between Shriver and Schwarzenegger has become increasingly strained as a result of his romance with Miley, who he began dating in November.

The tension between Schwarzenegger and Shriver has intensified as the Kennedys refused to welcome 22-year-old Cyrus into their family. Reports said the singer was also banned from joining her boyfriend at the annual Kennedy Christmas party.

"Maria doesn't want her there and won't budge," a friend told Life & Style. "She doesn't think it's appropriate to have Miley around the rest of the Kennedy family. Patrick insists on having her there -- or he will not come."

"They've been talking less and less. Every time they do talk, it ends up in an argument where Patrick is defend Miley," the source added.

Last Dec. 3, Maria Shriver had planned to attend the Art Basel Miami with her brother Anthony Shriver. However, Patrick Schwarzenegger's mom cancelled upon hearing that Miley Cyrus was scheduled to attend.

"Maria was going to go to Art Basel to spend some time with Anthony, but when she heard Miley was going to be there with Patrick, she cancelled," the source told BANG Showbiz.

Though Miley Cyrus and Maria Shriver still remained to be at odds, it appeared that Patrick Schwarzenegger has tried to work things out with his mom. On Thursday afternoon, 21-year-old Patrick enjoyed a rare moment without his girlfriend as he spent his time with his 59-year-old mom.

Schwarzenegger spent some quality time with Maria Shriver and his two sisters, 25-year-old Katherine and 23-year-old Christina. The family dined at The Ivy, a top restaurant in sunny Santa Monica. Before they departed, Patrick was seen hugging her mom.

Though Miley Cyrus and Maria Shriver still have a rift, Patrick Schwarzenegger has reconciled with his mom before Christmas comes. But will this mean that Miley and Patrick won't be spending the holidays together?