Moana concluded: “It brought us to the most beautiful little boy. You my little guy are perfect and your Mums love you.”
She and Isabella chose to pay homage to Moana’s Kiwi heritage with the name, which is a traditional Māori name that means fire.
It follows the couple’s decision to name their first child, a daughter, Svea in tribute to Isabella’s Swedish background.
“We don’t know which name we’re going with yet, but the names that we have selected are Māori names... that’s what we’re going with for this one, so that way we’ve got one of each,” Moana told WHO in April.
Moana included a series of photos from the hours after Ahi’s birth in her post, including snaps of her and Isabella admiring their son, a photo of her breastfeeding, and the moment Svea met her baby brother.
Isabella also shared a tribute to their newborn son on Monday, penning: “@moanahope you are incredible, I’m so unbelievably proud of you.
“You went to hell and back to get our beautiful boy safely to us. I don’t have words to describe what it feels like to share this experience with you and understand each other on such a deep level.
“You’re so strong and I love you very much. You’re such a natural and Svea and Ahi are so lucky to have you as their Mum. Ahi, we all love you so much everything and shines a little brighter now that you’re earth side.”
She shared many of the same photos Moana did, as well as a rare picture of herself breastfeeding Ahi and Svea at the same time.
Isabella’s sister, Emily Carlstrom, shared even more peeks at the latest addition to the family, posting photos of the moment she met Ahi on Instagram.
Meanwhile proud new mum Moana flooded her Instagram stories with clips of her baby boy cuddled up on her chest.
This was the first time Moana carried and delivered a child, as Isabella chose to experience pregnancy the first time around with Svea. Both children were conceived through IVF with the same donor sperm.