Credit: Twitter

Is Whitney Houston's daughter, Bobbi Kristina, 18, in more than just a casual relationship with her “brother” Nick Gordon, 22?

According to a source for Us Weekly, the quasi-siblings have taken things to the next level by getting engaged. "Bobbi Kristina is still so vulnerable since her mother passed away," the source says. "But Nick has become like her rock."

It was a rock of a different sort that got people talking in the first place: Bobbi has been photographed wearing a massive diamond engagement ring on her left ring finger, one that apparently belonged to her mother.

However, Nick told ABC News that he and Bobbi aren't hooking up — let alone engaged. "We're just close — just going through her mom's passing and grieving together," he explained.

Bobbi's rep has also refuted the engagement rumors, and a source for People adds, "She is just wearing her mom's ring."

Credit: Splash News/5min.com Photo: Bobbi Kristina and "Adopted Brother" Nick Gordon: PDA and Pizza in Atlanta on March 13, 2012

Sources: Us WeeklyPeople

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