(Cover) - EN Showbiz - Bobbi Kristina Brown's fianc has defended the pair's relationship against allegations of incest.

Whitney Houston and Bobby Brown's daughter announced her engagement to her "adopted brother" Nick Gordon in a recent promo for reality show The Houstons: On Our Own.

The couple got together following the February death of her mother, who had raised Nick but never formally adopted him.

Bobbi, 19, and Nick, 22, are left defending their status as a couple to disapproving family members in a newly-released clip from the show obtained by RadarOnline.

"Everybody else doesn't have to be in my business," Nick says. "The family has me out to be a bad person. Everyone gets it wrong, I was never officially (adopted) it's not incest."

The couple was subject to engagement rumours earlier this year but reportedly called off the plans due to timing issues.

Bobbi's aunt, Pat Houston, previously branded their relationship "unacceptable".

But the teenager steps up to echo Nick's proclamation in the new clip.

"I love him. They want to see us fail," she says. "I got one thing to say: You won't."

The Houstons: On Our Own airs on US television network Lifetime. (C) Cover Media