'My husband's mistress went into labour. Minutes later, my phone rang from the delivery room.'

We had two kids, a full life, and what I thought was a solid marriage. Then my husband got another woman pregnant — and asked me to help him become a father to her son.

I stepped outside the building to find a quiet place to take the call. My phone screen glowed with the name "Hubby" as I took a deep breath. He was calling from the US, and I knew the timing could only mean one thing: he'd become a father to a baby boy. I could hear the emotion in his voice despite the slight delay on the line.

"He's beautiful," he said.

"What's his name?" I asked.

He told me his name and I turned my eyes skyward, trying to stop the warm tears trailing down my cheeks.

"Where are you now?" I asked.

"I'm still at the hospital," he said. "You're the only person I wanted to share this with. I wish you were here."

You might be wondering… how did we get here?

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This is my husband of four years, partner of over a decade and father of our two girls. We had what looked like a solid relationship — tested across cultural and geographical boundaries, through the sleepless years of raising babies while we both pursued our careers.

We could talk about anything and everything. Heated debates about politics, gender, social and environmental issues were an aphrodisiac in our house.

He supported me going for my dreams and would take kind care of our girls without complaint — even if he was the only dad at a Frozen‑themed birthday party.

So in some ways, it made perfect sense that I was the first person he called at such a moment of joy.

But this baby was not something I could celebrate with him. I asked to see a photo out of a kind of perverse curiosity. Did his son look like his dad, or maybe even his sisters? Was there still a chance he was not the father? Or did he look like his mum — the woman with sharp cheekbones, macaroni curls and the glowing skin of someone under 30?

"The dreaded cliché."

I hadn't even known his mistress existed until three months before. Now she was part of our family story, her son, a brother to my girls.

My husband had sat on the side of our bed that Wednesday morning, staring at his hands as I came in to grab my clothes for the day.

If I had been paying attention, I might have noticed the faint line where his thick black wedding band used to sit, the new phone screen protector that blocked me from seeing caller ID or messages, and the T-shirt with sleeves tighter than usual around his biceps.

The dreaded cliché — "I need to tell you something" — came out of nowhere.

"I've been having an affair," he said.

I felt the air catch in my chest as I stared at him, my shirt half buttoned. My world slipped sideways, and then it slowly tilted all the way over as my husband continued.

He explained that he had started a relationship with his mistress nine months earlier — seeing her on regular work trips to the States — and that she had visited Australia once.

They worked together. Another cliché.

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My anger was quickly followed by total disbelief — not just at my husband's betrayal, but at his sheer stupidity. He claimed he didn't want the baby.

He told me he'd thought our marriage was over, but he didn't want to leave, so he started auditioning for a replacement just in case.

It all hit me like an emotional set of massive waves, smashing me into the sand again and again.

I tried to hold our family together when my husband returned to the US because he wanted to be there when his mistress gave birth.

How I longed for the oblivion of ignorance in the weeks before his son entered the world. I went to sleep at night picturing my husband nesting with another woman.

During the day, I tortured myself reading back through their texts and emails I now had access to. I put on a brave face in front of colleagues, friends and the school mums, sidestepping their questions about my husband's travels with what felt like stone shoes on my feet.

The date of his son's birth may as well be tattooed across my chest; it is now permanently part of my story. It marked the start of a new chapter in our marriage as we attempt to create a family for all of my husband's children.

*The author of this article is known to Mamamia but has chosen to remain anonymous for privacy reasons.

Feature Image: Getty. (Stock image for illustrative purposes).