Meanwhile, Ryan also delighted in his son's arrival on his own Instagram, writing: "It’s a boy!"
"At 0332 on the 23rd of May we were gifted with our beautiful baby boy, now known as Kit!! My heart must have grown upon seeing him as I thought It was already full, but alas I love him so much already," he said.
"Witnessing the birth was again truely amazing and has me in ore of Morgan. Seeing Kit receiving kisses from his brothers is true joy. We are meant to be parents of sons! Welcome to the family Kit James Gruell."
Morgan and Ryan, who tied the knot in a beach-side ceremony in Noosa in 2016, are already the proud parents to Taj and Flynn, aged one and three.
Their newest family addition makes them a perfect family of five, with Morgan's mum Lisa clearly delighted at becoming a grandmother for the third time around.
Her joy was made apparent when she commented on her daughter's post, adding a bittersweet mention of her late daughter Jaimi Kenny.
"Morgan my beautiful… look at your gorgeous little family. I love you all so much and Jaimi would so love this too xxxxx Kit James xx," Lisa said.
Former professional dancer Morgan first revealed her pregnancy in an Instagram post last year, where she shared photos of her sonogram and of her growing bump.
"Life is crazy - we might as well stay in the crazy!" she captioned the news. "Baby #3 due end of May!"
Ryan also shared a photo of the sonogram and wrote: "Our family is growing by another. Flynn and Taj are going to share the role of big brother at the end of May when we welcome another Gruell into the world."
"We were so happy to see a perfectly happy and singular baby developing at our 12 week scan," he added.
"True to form to Morgan continues to amaze me with her capacity to love and care for the boys and I (including my FIFO fathering), while also dealing with the fatigue, sickness and soreness that the first trimester has brought."
Now as a family of five, there's no doubt that Morgan will be supported by her mum Lisa, who often shares snippets of her "grannie duties" to social media.
"Weekend with Grannie and our farm animals," Lisa captioned a series of snaps with her family and of her grandson Flynn. "This beautiful little fella…. thank you Momo & Ryan. #grannieandflynnandtaj."
It's safe to assume that Lisa's grandchildren will continue to make regular appearances on her Instagram, only now they'll also feature Morgan's new bundle of joy.