Nick Lachey ​and Vanessa Minnillo expecting second child

Nick and Vanessa Lachey attend the "Game Of Thrones" Season 4 New York premiere at Avery Fisher Hall, Lincoln Center on March 18, 2014, in New York.

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Nick and Vanessa Lachey (formerly Minnillo) are expecting their second child together.

The 98 Degrees star revealed the baby news Tuesday on Twitter, showing off a picture with the words: "It's a girl":

Nick, 40, and Vanessa, 33, already have a son, Camden John, who was born in September 2012. They wed in 2011.

Last year, Lachey spoke with CBS News about what it's like being a first-time dad: "It's an amazing journey and it truly is a journey. Every day there's something new and different that he's doing or that's happening. I've just learned to enjoy every moment for what it is and take it all in. It's been an amazing ride so far truly, and it's only just started."