"This is his worst nightmare," the family member says.
His ex-wife and Bobbi Kristina's mom, Whitney Houston, died under similar circumstances almost three years ago, so Brown, 45, is particularly distraught.
"Losing Whitney was hard, but this is a million times worse," source says. "And to lose her in the same way would devastate him."
While relations between members of the Brown and Houston families may not have always been perfect, they are putting aside tensions and rallying around the 21-year-old.
"This is not the time for family feuds," the family member says. "It doesn't matter what happened in the past. All that matters is that everyone's here for Krissy."
Celebrities and family members alike have expressed their love and support, and "all family interactions have been positive."
"No one is holding any previous grudges," the family source says.
Brown added in a statement on Sunday, "Please allow for my family to deal with this matter and give my daughter the love and support she needs at this time."
Reporting by STEVE HELLING
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