Our brightest golf star just stepped aside from sport to be with his terminally ill mum.

It can be easy to forget that sports stars, however remarkable, are just people.

Australian golfer Jason Day has always said without his mum Dening, he’d never have made it to number one in the world, and now, at the height of his career, he’s stepping aside because she needs him.

The 29-year-old broke down today in front of a room full of journalists as he announced he would be taking indefinite leave from the sport he loves, because the woman he loves above all else is sick.

“[My mum] has lung cancer. At the start of the year, she was diagnosed with 12 months to live,” he said, fighting back tears.

“She’s going in for surgery this Friday and it’s really had to even comprehend being on the golf course right now because of what she’s gone through,” he said.

Day is currently number three in the world, but he walked off the course just six holes into the opening round of the World Matchplay Championship in Austin on Thursday.

Some speculated the defending champion may be injured, but he was simply feeling the toll of his mother’s potentially terminal illness.

Earlier this year, she was given a year to live when a 3-4cm mass was discovered on her lungs, according to the PGA Tour website.

Last week, Day flew her to the United Stated so she could have more tests done by doctors in Columbus, Ohio, who are cautiously optimistic emergency surgery could prolong her life.

“Emotionally it’s been wearing on me for a while. And I know my mum says not to let it get to me, but it really has," Day said.

“So I just need some time away with her to make sure that everything goes well because this has been very, very tough for me."

The news is all the more heartbreaking as Day's father, Alvyn, died from stomach cancer when he was just 12-years-old.

He had been an abusive alcoholic, and the family was never wealthy, but Dening sacrificed everything she could for her kids.

When Day, having just crossed the cusp of adolescence, went off the rails and began drinking and fighting, his mum borrowed money to have him shipped off to a boarding school known for its golf academy.

“So I’m going to do my best and try and be there the best I can for her, because she is the reason that I’m playing golf today," Day said.

“Family is first and it’s just — it’s just a hard time.”

Many have shared their support for the family on social media:

We wish Jason and Dening all the best during this difficult time.