Oprah Winfrey has snagged the interview everyone must have been vying for ... Sorry Matt Lauer! Sorry Kelly Ripa! ... The Queen of Daytime will sit down with Whitney Houston's 18-year-old daughter Bobbi Kristina for a March 11 chat on Oprah's Next Chapter on her network OWN.

The one-hour special will also include interviews with the late singer's sister-in-law/manager Patricia Houston and her brother, Gary Houston.

There has been much speculation about Bobbi Kristina's health since her mother's passing, particularly after she was hospitalized twice in the days following Houston's February 11 death. Then, Bobbi Kristina went missing in the hours after her mother's funeral but was later said, by a family member, to have been spending time alone to collect her thoughts.

Various reports claim the teen is haunted by the same addictions that led to Whitney's declining health -- some reports have even asserted that Houston did drugs with her daughter at times.

We bet Oprah will ask ALL the questions we all want to hear the answers to ... we'll tune in March 11th!