Alex's wife, Bonnie, also put up her own post.
"Look who's finally arrived! Welcome to our beautiful baby boy (name TBC 😂)."
"Baby Cullen arrived in the early hours of Sunday 15/8/21 and @alextcullen and I are besotted," she penned.
"Can't wait to introduce him to our girls. Three under three - fun times ahead."
Not long afterwards, Alex shared his own post.
"We couldn’t be happier," he wrote in his caption.
"Our healthy, happy little boy came into the world at 1.08 on Sunday morning weighing 3.7 kilograms. After 41 and a half weeks it was well and truly worth the wait!
"Name TBC and can’t wait for his big twin sisters Audrey and Evie to meet him, boss him and shower him with cuddles. I marvel at Bonnie’s strength especially in these very trying times. Just amazing. Mum and baby Cullen recovering well."
The new addition is the third child of the proud parents who welcomed twin girls, Audrey and Evie, back on January 20th, 2019.
Sharing a photo of the first-time parents clutching their newborns in the hospital, Alex wrote on Instagram "Our new family. Our beautiful girls were born in the very early hours of January 20. Mum is doing great. Girls are too. We couldn’t be happier."
Just over two years later, the presenter announced his third child was on the way in the most casual way possible - much to the shock of his morning show family.
Chatting live on air to fellow Today presenters Karl Stefanovic and Allison Langdon about Tasmania's Wine Glass Bay, Alex revealed the stunning location was one of his first getaways with Bonnie.
Ally then joked, "They've now had twins, they're married, I'd say the trip went well."
At this point, the sports presenter revealed the big news: "Hey, I should say, Bonnie's pregnant!"
Jaws dropped as Karl yelled "Whaaaat?!" and Ally cheered with joy.
"I meant to tell you that. Sorry." Alex continued, as casually as if he was discussing the weather.
"Yeah, yeah, another one on the way, which is extremely stressful," Alex said with regards to having just welcomed Audrey and Evie.
"Slightly earlier than we'd planned and three under three will be a challenge but we've over the moon!"
Congratulations to the proud parents!
This article originally featured on our sister site, New Idea.
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