Grammy Award-winning singer Beyoncé Knowles-Carter has finally opened up and discussed the painful experience of trying to conceive a child, including details of a miscarriage she suffered two years ago.

The 31-year-old singer is married to rapper Jay-Z and is normally very secretive about her personal life, particularly with regard to the couple's one-year-old daughter, Blue Ivy Carter.

In a forthcoming HBO documentary about the Halo singer's life, titled Life is But a Dream, Beyoncé spoke about the emotional heartbreak she went through when she miscarried.

"About two years ago, I was pregnant for the first time," Beyoncé said, "And I heard the heartbeat, which was the most beautiful music I ever heard in my life."

"I picked out names, I envisioned what my child would look like . . . I was feeling very maternal," she recollected, adding that something went wrong in the early stages of her pregnancy. And at a routine doctor's visit, Beyoncé found out she had lost the baby.

"I flew back to New York to get my check up -- and no heartbeat," she said, "Literally the week before I went to the doctor, everything was fine, but there was no heartbeat."

Beyoncé, who recently reunited with former Destiny's Child band mates Kelly Rowland and Michelle Williams, ahead of the Superbowl performance, admitted it was the most heart-breaking thing in her life.

"I went into the studio and wrote the saddest song I've ever written in my life," she said, although she did not mention the name of the track, "And it was actually the first song I wrote for my album. And it was the best form of therapy for me, because it was the saddest thing I've ever been through."

The loss was first revealed by Jay-Z, who mentioned in a track called Glory. The song was released shortly after the birth of Blue Ivy Carter on 7 January.

And as far as her daughter is concerned, Beyoncé denied speculation she was never actually pregnant and faked the whole event, while a surrogate carried Blue Ivy. And the best way of emphasising those denials - the pop star is also releasing her actual sonogram video to the public.

"Being pregnant was very much like falling in love," Beyonce said, "You are so open. You are so overjoyed. There's no words that can express having a baby growing inside of you, so of course you want to scream it out and tell everyone."