Cissy Houston is reportedly vowing to fight Bobby Brown's attempts to gain control over his daughter's $20 million estate all the way "to the grave."

According to the Atlanta Journal Constitution, the 46-year-old "Every Little Step" singer filed legal documents last week seeking to gain legal guardianship over his daughter's finances.

Bobbi Kristina Brown, 22, has never regained consciousness since being found face down in a bathtub and unresponsive in a Georgia home she shared with boyfriend Nick Gordon in late January. Her $20 million fortune stems from monies placed in a trust for her by her mom Whitney Houston.

Shortly after Brown made his intentions known, Cissy Houston released a statement asserting that "this is a family matter" and has refrained from publicly saying much else since then.

But a source described as close to the family told Radar Online, "Cissy Houston will fight this to the grave." The source added, "Since day one, all of the Houston's have been waiting for Bobby to try and get Bobbi Kristina's money and they knew it was just a matter of time. No one is surprised that he is making a grab for her money."

Those close to Brown vehemently deny any of his actions are motivated by money, instead arguing he's simply interested in doing what's best for his daughter and making sure she has the kind of long-term health care service doctors have indicated she will need.

"Bobby is Krissy's father," a source from his camp told People. "He only wants what's best for her. This is not about him taking her money -- he has money of his own."

Since Bobbi Kristina has been hospitalized police have launched a criminal probe of the circumstances surrounding her ordeal after finding several unexplained bruises on her body. TMZ has reported the probe targets Gordon as a primary suspect.