Toni Street on her new book Lost and Found, surrogacy, and grieving her siblings

Toni Street with her fellow Coast presenters Sam Wallace and Jason Reeves. Photo / Instagram

Toni Street gets honest about her life in her new book - and she's is letting the public in on some of her toughest moments.

Street touches on grief, her auto-immune disease and her surrogacy journey in her memoir Lost and Found.

"I think people have widely known that I've lost siblings, but I don't think they've got any idea of the detail, how it happened and the impact it had on my family," she told Newstalk ZB's Mike Hosking.

The Coast Breakfast presenter says writing the book was a cathartic experience, and it was her Mum who encouraged her to tell her story.

"I was really nervous about that because I didn't want to upset my parents any further and make them relive what happened. But I think it's important to because when you have children dying in a family it's not something you sit around and talk about a lot - it's too painful for everyone. So I think it was really good for all of us to do that, properly now with years under the belt."

Toni and her twin brother Lance were the much-loved first children of Taranaki dairy farmers Geoff and Wendy Street. At 9 months old, Lance was diagnosed with acute myeloid leukaemia, passing away a year later. Devastated but determined to give Toni another sibling, Wendy became pregnant soon after Lance's death, but after a difficult pregnancy, their baby Tracy was born, but only lived for a couple of hours.

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She explained to Hosking one of the book's key themes is how she and her family dealt with the grief.

"I still don't know how we really did it to be honest," she says.

"I didn't handle it particularly well I kind of denied it was happening, got on with my life. And then it rears its head years later. Where you're forced to deal with it."

Street had a very rural upbringing, and both of her parents grieved in different ways.

"Mum got quite angry at Dad for a while there that he pushed on and was super positive when actually she just wanted to be sad," she says.

As well as soldiering on after a childhood filled with grief, Street faced health challenges later in life when she was diagnosed with Churg-Strauss Syndrome after giving birth to her second child.

She had her gallbladder removed and is on permanent medication, and despite this lives her life to the fullest.

However she says the liver disease she contracted after antibiotic reaction "knocked her for six".

Because of her autoimmune disease, Street turned to surrogacy when she wanted to have another child.

"It's a completely broken system. It's the adoption act - you shouldn't be adopting your biological child," she explained.

"The big thing - and I just made a submission to the law commission - for me, is when that baby arrives, the legal rights at that moment should be the intending parent, as you have decided nine months earlier with your surrogate, but they're not."

Listen to Toni Street's full interview with Mike Hosking below:

• Lost and Found goes on sale in October.