Seal: Heidi Klum and I "Are Having a Girl"

Seal announced the sex of his wife's fourth baby on a taping of The Oprah Winfrey Show Friday afternoon.

"She can't keep a secret," Seal says, adding that his wife said he could start telling people they're expecting a girl. (Seal also first confirmed she was pregnant again at a NYC concert.)

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In Klum's first interview about her pregnancy, she revealed to Us Weekly she was hoping for a girl.

"We'd be happy with either," she told Us. "Bu would be a lie if I said we all weren't hoping for a little girl -- especially Leni, because she would love to have a little sister.

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The Project Runway host and Seal are raising Leni, 5 (dad is Italian businessman Flavio Briatore), Henry, 3, and Johan, 2.

The couple is celebrating their fourth anniversary this Sunday.

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"We're going to get married again," Seal tells Oprah. "So this is going to be the fourth time, our fourth anniversary. The fifth time, and I'm not quite sure what the theme is.

"You know what my wife's like," he continues. "She's always got some trick up her sleeve, bu going to be a good get-together, you know, lots of friends."

Seal and Klum got engaged on Christmas Eve 2004. They tied the knot five months later on May 10, 2005 on a beach in Mexico.