It's official - Kiwi heart-throb Martin Henderson is off the market.

He is seeing 47-year-old director/producer and arts patron Helen Randag. And it's love.

The notoriously private Greys Anatomy star took to Instagram to announce the news, posting a photo of the two of them simply captioned "Out with my bae - I love you darling."

Randag replied, posting "I love you too my darling."

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The reaction from his 179,000 followers was mostly positive with most congratulating the pair, while a few expressed their devastation.

"Its about time - Marty needs someone in his life," posted one.

Others, however, said they were "crying".

Originally from England, Randag studied fine art in London.

At just 24, after receiving an inheritance from her art collector grandfather, she set up a charitable foundation to support the arts in honour of him. In 2010 she was awarded the Prince of Wales medal for Arts Philanthropy, the youngest ever recipient of the award.

Previously married, she now lives in California and has her own film production company, Midheaven Productions. In 2014 she wrote, directed and produced a short film Portrait of a Star, which premiered at the New York City International Film Festival.

She has recently been appointed a board member of the Los Angeles Institute of Contemporary Art.

Henderson, 42, burst on to New Zealand screens at just 17 years old, playing Stuart Neilson in Shortland Street. While that role only lasted three years, it was enough to establish him as a bona fide star.

Martin Henderson in the early days of Shortland Street, with L-R Michael Galvin, Craig Parker and Temuera Morrison. Photo / Supplied
Martin Henderson in the early days of Shortland Street, with L-R Michael Galvin, Craig Parker and Temuera Morrison. Photo / Supplied

He has since gone on to a successful career in Hollywood, working with the likes of Naomi Watts, Jennifer Garner, Cate Blanchett, Charlize Theron and Jake Gyllenhaal.

He is now heating up screens in the US starring as Dr Nathan Riggs in Greys Anatomy. Despite having been in the spotlight for 25 years, Henderson has managed to keep his private life very much private.

Martin Henderson is currently starring in Grey's Anatomy. Photo / Getty Images
Martin Henderson is currently starring in Grey's Anatomy. Photo / Getty Images

He has been linked in the past to Hollywood actresses Demi Moore and Jennifer Garner, but has never gone public with a relationship - until now.

In a candid interview with the Herald last year, he said he'd love to get married and become a father.

"I've always wanted kids, but I never felt ready. I wasn't mature enough to have them earlier. It would've felt more of a burden, whereas today I'm at an age where spending time with kids or my nephews is wonderful. But I'm not going to rush out and do it for the sake of it.

"I don't think having a family is the answer to anything, but more a complement to life. I'd rather find the right woman first, but life's funny - I might find someone and they can't have kids. So I don't want to get hung up on the idea because then if I met someone who couldn't, I'd feel like I was being denied something."

Henderson will next appear in the horror movie Strangers 2 with Mad Men star Christina Hendricks, due to be released in 2018.