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Mark-Paul Gosselaar, Catriona McGinn

Michael Bezjian/WireImage.com

Mark-Paul Gosselaar's family tree is starting to sprawl.

A baby is on the way for the Franklin & Bash star and wife Catriona McGinn in September, People reports. The wee one will be the couple's first child together—and Gosselaar's third overall.

"We are all really excited for the arrival of our new addition," the actor told the magazine. "We've always wanted a big family. The kids are looking forward to a little sibling, and are asking a lot of funny questions right now."

The former Saved by the Bell preppy has two kids, 6 1/2-year-old daughter Ava Lorenn and 9-year-old son Michael Charles, with ex-wife Lisa Ann Russell—aka the current Mrs. Jeff Probst.

The Survivor host dished to Larry King in December about sharing custody of his wife's little ones with Gosselaar and McGinn—and it sounds like tribal rivalries are nothing he has to worry about on the homefront.

"They raised them with the kind of love that the kids they see me, and he's now remarried, his wife, [the kids] just see us as two more parents," Probst said.

Gosselaar and McGinn tied the knot last July.