Rosie Batty shares a heartbreaking tribute to her son on what should be his 15th birthday.

On February 12, 2014, Luke Batty, then 11 years old, was murdered by his father while at cricket practice in Melbourne.

The very next day, his mother, Rosie Batty, began a public campaign to raise awareness of family violence. She has since become one of Australia’s most respected voices on domestic violence, working tirelessly to ensure no other family or mother has to endure what she and Luke had been through.

Yesterday, had his life not been tragically cut short, Luke would have celebrated his 15th birthday.

Posting on the Luke Batty Foundation's Facebook page, Rosie shared a heartfelt message for her son on his special day.

"Happy birthday to my beautiful Luke. We all miss you so much," Rosie wrote.

"I am celebrating you today. There's an entire community campaigning for change in your memory. We've achieved a lot since we started Never Alone two years ago to this day.

"I know you'd be really proud of us. From Mum."

Others shared their own messages of support and thanks for Rosie and Luke on her post.

"That boy is changing Australia with the help of his Mumma," one woman wrote.

"Happy Heavenly Birthday Luke. You have an amazing mumma. And we are all so proud of her," another posted.

LISTEN: Maria Lutz and her two children were gassed in their home by her husband. It’s the tragedy that stopped us in our tracks. (Post continues after audio...)

The year after Luke's death, Rosie was presented with the 2015 Australian of the Year Award.

During her acceptance speech, she said, family violence "is an entrenched epidemic that we've lived with since time began, so we've got a long way to go."

But, she added, "I do believe the tide is turned. It's no longer a subject that only occurs behind closed doors."

If you or someone you know is in need of help, please call the National Sexual Assault, Domestic and Family Violence Counselling Service on 1800 RESPECT.