New Zealand actress Antonia Prebble has given birth to a "beautiful boy".

The Westside matriarch announced the arrival of her newborn baby boy on Facebook this evening, posting:

"Dan and I are so delighted to share that our beautiful boy is now with us in the world.

"Freddie John Musgrove was born just over a week ago and is adjusting really well to his new digs outside my belly - and Dan and I are completely besotted," she wrote.

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Dan and I are so delighted to share that our beautiful boy is now with us in the world. Freddie John Musgrove was born...

Posted by Antonia Prebble on Sunday, 21 July 2019

The post is accompanied by a photo of the little one's hand grasping at a finger, and has so far had over 2400 reactions from Facebook fans.

Prebble, best known for her role as Outrageous Fortune's Loretta West, now plays the lead role of Rita West in Westside, a prequel to Outrageous Fortune.

She is engaged to fiance Dan Musgrove, who plays Lefty Munroe on the show.

The couple also used social media to announce their engagement in July last year.

Prebble worked right up into the last weeks of her pregnancy, and spent shoots covering up her own burgeoning baby bump. This meant the costume department had to produce innovative ways to mask the pregnancy.