The 71-year-old singer, who is best known for her hit songs 'Walk on By' and 'I Say a Little Prayer', said that Houston was "happy" and "ready" for a comeback just before she passed away in the bathroom of her hotel room on the night of Clive Davis's pre-Grammys party last month.
Warwick told Good Morning America: "I spoke to Whitney the day that she passed. I spoke to her that morning. She said, 'You're here, aren't you? You're coming to the party, aren't you?'
"I said, 'Yeah, I'm going to be there', and she said, 'Thank you, I want you to be here. You've got to be here for me'. I spoke to her that afternoon and that was it."
Referring to Houston as "the little girl [she] never had", Warwick added: "She was so up and ready and happy. She had everything in the world to live for. She had a new film that was an absolute dream to make and do. She was getting ready to go back into the studio to record. She was getting her vocals together."
Warwick described Houston's death as "very, very surreal", saying: "It hasn't really sunk in yet. I have not had an opportunity to really mourn or completely break down, which I will do, I know that."
She said of Houston's mother Cissy: "I am so proud of her. She's really holding up so very well. She has her moments, of course, and will continue to have her moments. I think she's coming to terms with it just about now. It's going to take quite a bit of time."
Warwick also said that she will support Houston's daughter Bobbi Kristina Brown through the mourning process, adding: "That's the one thing I love about my family. We are family. She has the support that she actually needs."
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