Bobbi Kristina is reportedly dating Whitney Houston's "adopted son," and grandmother Cissy isn't having any of it.

Whitney's mom thinks the young romance is "incestuous," and believes 22-year-old Nick Gordon is taking advantage of the grief-stricken Bobbi Kristina, a close friend told TMZ.

The late singer took in and raised Gordon over 10 years ago, but never legally adopted him.

Bobbi Kristina and Gordon fueled dating rumors after they two were spotted kissing and holding hands in a Target store in Georgia last week, according to HollywoodLife.

While 19-year-old Bobbi Kristina and Gordon refer to each other as siblings -- "brudder" and "lil sis" -- Gordon made it clear last night that they're not related, tweeting about Houston, "For the stupid ppl out there she gave birth to 1 child. And she trusted me with EVERYTHING!"

He added, "She called me her "God Son" I swear some ppl in this world act like they don't have a brain..."

However, Houston's so-called "adopted son" denied reports the two are an item.

"We're just close -- just going through her mom's passing and grieving together," Gordon told ABCNews.com.

Tags: Whitney Houston