It's a beautiful day in the house of the actor best known for his role as Zack Morris in "Saved by the Bell," as Mark-Paul Gosselaar's wife Catriona McGinn, with whom he's been married since 2012, has just given birth to the couple's second child - and Mark-Paul's fourth altogether!

The first Mark-Paul Gosselaar wife, former model Lisa Ann Russell, married the actor in 1996 and divorced him in 2011, and they had two children together: Michael, who's now 10 years old, and 8 year-old Ava, and he shares his kids' custody with ex Russell.

According to The New York Daily News, Mark-Paul Gosselaar wife gave birth to a beautiful baby girl last Tuesday night, announcing the happy news after posting one of the most adorable baby pictures in the history of Instagram, saying the newest member of the Gosselaar family was named Lachlyn.

Entertainment Tonight reports that the couple announced that Mark-Paul Gosselaar's wife was expecting their second child last December, as Catriona was already well into her pregnancy, after the couple had their first child together, a son named Dekker Edward, back in September 2013 - so now they have their little set, a boy and a girl!

Before posting the adorable picture on his Instagram page, the actor took to Twitter to reveal the news, Perez Hilton reports.

"So in love with our new baby girl, Lachlyn!" he tweeted, happily announcing the big news coming out of his house from earlier this week. "Born last night 2/17 Mum and baby are healthy and happy. 2 boys, 2 girls, too perfect!" he finished, speaking about the fact that he has two of each!

Of course, they're all incredibly happy right now, but they'll be hosting a busy house now with a baby and a toddler around - but surely Mark's biggest children will be able to help out!

Congratulations to Mark-Paul Gosselaar and wife Catriona McGinn!