It's a girl!

Mark-Paul Gosselaar and his wife, Catriona McGinn welcomed their baby girl, Lachlyn, into the world on Tuesday, Feb. 17. This is the 'Saved by the Bell' alum's fourth child and his second with Catriona.

"So in love with our new baby girl, Lachlyn! Born last night 2/17 Mum and baby are healthy and happy. 2 boys, 2 girls, too perfect!" the 40-year-old actor wrote on his Twitter page.

mark-paul gosselaar family

Mark with his family in October 2014.

Last December, Mark-Paul and Catriona confirmed they were expecting a new addition to 'Us Weekly.' "I'm very excited!" the proud papa said. "We have told our families [the baby's gender], but we haven't told them the name."

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The couple — who wed in 2012 — are already parents to son named Dekker Edward, whom they welcomed in October 2013. Mark-Paul also has two older children, Michael, 10, and Ava, 8, from his first marriage to Lisa Ann Russell.

Congratulations to the Gosselaar family!