Content warning: This post contains details some readers may find triggering.

It was the day before his 34th birthday. A Sunday morning like any other.

Walter Mikac kissed his two pyjama-clad little girls and wife goodbye before heading off to play golf.

He was hosting a local tournament on the sprawling greens of a course in Tasmania. His wife, Nanette, and young daughters, Alannah, six, and Madeline, three, decided to have a picnic at the local historic site of Port Arthur where Nanette often volunteered as a ghost tour guide. They planned to meet up later that day.

Walter Mikac with his family. Image supplied.

They never got to meet up. That morning farewell would be the last time he ever saw his family.

Speaking on Wednesday's episode of Anh Do's Brush With Fame,Walter, now 56, recalled what happened that afternoon on Australia's darkest days in history - the Port Arthur massacre - pinpointing the moment he realised his family had been ripped away from him in an unfathomable act of evil.

Walter jumped in his car and drove to the site, his golf mates by his side, where he was met with the nightmarish result of 29-year-old Martin Bryant's killing spree.

Then came the waiting.

He remembers pacing up and down the room, his heart sinking in his chest as the clocked ticked on through to early evening, still without answers.

Eventually, a woman named Pam, the local doctor and a friend of the family delivered the news no one wants to hear: Nanette, Madeline and Alannah had been murdered.

Through the depths of his grief, the passionate anti-violence advocate managed to make an impact on the world - he relentlessly campaigned to have Australia's gun laws tightened after Martin Bryant was able to slaughter 30 people with an automatic rifle that Sunday.

Walter Mikac. Image: ABC.

He became a guiding force in lobbying for the strict gun control laws Australia is now known for.

Last year, he toldMamamia: "What happened 22 years ago was amazing because I was recently looking back at some old papers... my parents had kept all the old papers from that time... and I noticed on May 11, the gun laws had passed and the gun buy back had begun. That all happened in 12, 13 days.

"I don't think anything could happen that quickly almost ever again, and a few things helped that. One was that John Howard had just been newly elected and had a pretty big majority and then also, the fact the country was just so shocked."

Today, Walter lives and works in NSW's Byron Bay with his 17-year-old daughter, Isabella. The charity he built in the year after Nanette, Alannah and Madeline died - The Alannah and Madeline Foundation - still works tirelessly to protect children from violence.

He still thinks of his wife Nanette and his girls often, and hopes to see them again one day.

You can watch the full episode of Anh Do's Brush With Fame with Walter Mikac on ABC iView.

If you or someone you know is going through grief, depression or the loss of a child, please seek professional medical advice, or contact Lifeline on 13 11 14. If you are in immediate danger, call 000.