Whitney Houston's mother is furious that the late singer's daughter has tied the knot.

The "Greatest Love of All" hitmaker's only child Bobbi Kristina Brown recently insisted she had secured her grandmother Cissy Houston's blessing before she married her long-time beau, Nick Gordon, last week, but friends close to Cissy have admitted she had no idea about their wedding in Atlanta, Georgia, before it took place.

A Houston family insider told gossip website TMZ.com that Cissy was angry when she found out the couple, who were raised as brother and sister after Whitney informally adopted Nick when he was 12, had got married but has realized there is nothing she can do about it now.

Bobbi, 20, and Nick, 24, previously claimed that they got Cissy's approval before exchanging vows and she was "very happy" for them. "We saw her at our cousin's sweet sixteen and she gave us her blessing," Nick added.

But the source said that neither Bobbi nor Nick ever asked Cissy for her blessing.

Aspiring singer Bobbi, who is gearing up to release her debut single, has had a troubled relationship with her grandmother since she urged people to boycott Cissy's book Remembering Whitney, which addressed the late star's drug abuse, last year.

Bobbi and Nick's unconventional love was met by widespread disapproval from their family members and Cissy penned an open letter questioning whether he was good enough for her granddaughter last July.