R&B singer Bobby Brown says his daughter, Bobbi Kristina Brown, was “an angel” and that the family must find a way to honour her memory.

Bobbi Kristina, the daughter of singer Whitney Houston, died on Sunday in hospice care, six months after she was found face down in a bathtub in her suburban Atlanta home. Authorities are investigating her death.

“Krissy was and is an angel,” her father said in a statement. “I am completely numb at this time. My family must find a way to live with her in spirit and honour her memory. Our loss is unimaginable.”

Bobbi Kristina had been in hospital for months in Atlanta – eventually being placed in hospice care – after being found in a manner grimly similar to the way her megastar mother died three years earlier.

A police report earlier this year described the incident as a drowning. In a statement on Monday, the Fulton County Medical Examiner’s Office said a post-mortem will be needed to evaluate what led to the death of Bobbi Kristina, but the time that has elapsed since will complicate the investigation.

The medical examiner did not release a timeframe for the post-mortem but said additional lab testing might take several weeks. “Interpretation of autopsy findings and other information will also be challenging,” the medical examiner’s office said. “However, an autopsy could be helpful to address questions which may arise about the cause of her unresponsiveness and eventual death.”

Nick Gordon, who shared her home with her, said at the time it seemed Bobbi Kristina wasn’t breathing and lacked a pulse before help arrived.

Born and raised in the shadow of fame and litigation, shattered by the loss of her mother, Bobbi Kristina was overwhelmed by the achievements and demons of others before she could begin to figure out who she was.

As the news of her death spread across social media, several celebrities tweeted their condolences.

Houston sold more than 50 million records in the US alone during her career. Her voice, an ideal blend of power, grace and beauty, made classics out of songs like Saving All My Love For You, I Will Always Love You and The Greatest Love of All. She earned six Grammys and starred in the films The Bodyguard and The Preacher’s Wife.

Bobby Brown, who had a bad-boy image, also became a huge star, selling platinum records before drugs and legal woes derailed his career.

After their divorce in 2007, Houston kept custody of Bobbi Kristina and raised her alongside Gordon, an orphan three years older than her daughter.

The threesome’s tight bond was shattered when Houston’s assistant found the singer’s lifeless body face down in a foot of water in her bathtub at the Beverly Hilton Hotel just before the Grammy Awards in 2012.

Bobbi Kristina, then 18, was at the hotel and became so hysterical she had to be taken to hospital.

She and Gordon then went public with their romance, posting defiant messages online after the tabloids accused them of incest.

Relations between Gordon and some other relatives soured over the past year.

On June 24, Bobbi Kristina’s court-appointed representative sued Gordon, accusing him of misrepresenting his relationship with Bobbi Kristina. The complaint accused him of being violent towards her and taking more than $11,000 from her account while she was in a medically induced coma.

The lawsuit also accused Gordon of assault, battery, intentional infliction of emotional distress, unjust enrichment and conversion.

Fulton County District Attorney Paul Howard said he and his office are interested in reviewing the investigative file to determine whether any charges will be filed.

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