Third Child on the Way for Mark-Paul Gosselaar

He and and wife Catriona McGinn "are thrilled to announce they're expecting their first child together in September," the Franklin & Bash star's rep tells PEOPLE exclusively.

Elizabeth Messina

There’s a baby on the way for Mark-Paul Gosselaar.

He and and wife Catriona McGinn “are thrilled to announce they’re expecting their first child together in September,” the Franklin & Bash star’s rep tells PEOPLE exclusively.

Gosselaar, 39, wed advertising executive McGinn, 34, last July in Santa Ynez, Calif.

The actor is already dad to two children — daughter Ava Lorenn, 6½, and son Michael Charles, 9 — from a previous marriage.

“We are all really excited for the arrival of our new addition. We’ve always wanted a big family,” Gosselaar tells PEOPLE.

“The kids are looking forward to a little sibling, and are asking a lot of funny questions right now.”

— Sarah Michaud with reporting by Julie Jordan