Libby welcomed baby Alfie into the world on May 17th, taking to her Instagram to share the happy news.
"He's here" she captioned the post with a photo of herself, her husband Luke, and of course her bouncing baby boy post-delivery.
"The final piece to our family puzzle (for reals this time!)" Libby added.
"Alfred Sunny Trickett arrived at 9:09am on the 17th of May via an elective cesarean birth, weighing 3.5kg and 52cm long."
"Every birth I've had has been extraordinary and this one was no different. Calm, full of joy and laughter, I couldn't have asked for a better way to meet our baby boy."
"Alfie has no idea what he's in for with his three big sisters and the girls are absolutely smitten."
Libby then added a hilarious hashtag to the end of her caption "#alreadyweedandpooedalloverhimself."
After suffering a miscarriage in August 2014, Libby welcome daughter Poppy Frances Trickett into the world on the 31st of August 2015.
Her second daughter - Edwina Daisy "Eddie" Trickett, was born on the 23rd of February 2018, whilst her third daughter - Bronte Rose Trickett - was born on the 7th of November 2019.
And in an amusing twist of fate, after declaring she was "finished having children" on The Morning Show in 2021, she announced that her and husband Luke were expecting baby Alfie in December 2022.
Whilst she is known as an Australian swimming legend, there's no doubt that out of the pool Libby has been (and will continue to) nail motherhood.
"Our family isn't perfect but we work every day to be better. I'm grateful for my tribe, you have certainly made me a better human," Libby captioned a previous Instagram post with her kids.