Nigel Foote was strumming his guitar when his son Lachlan walked by and was stopped in his tracks by the beauty of the tune he was composing.
"That's pretty, Dad," the 21-year-old said, gently resting his hand on his shoulder.
It was the last conversation they would have, before Lachlan's senseless and tragic death on the bathroom floor of the family's Blackheath home several hours later.
"I can almost feel his hand on my shoulder now as I tell you the story," Nigel told news.com.au.
The bright, sporty and musically gifted young man blacked out and never regained consciousness in the early hours of New Year's Day in 2018, a day before his birthday.
Nigel has spoken of Lachlan's final hours — both in tribute to his son's life and as an urgent warning to others about the seemingly innocent substance that killed him.
"He headed off from home at about 6.30pm and took the train into Katoomba to meet some mates to celebrate New Year's Eve," Nigel recalled.
"They spent a few hours at the Harp and Fiddle pub there. People came in and out, they just had a nice evening catching up and chatting. He left at about 11 but met a bunch of workmates who were just arriving, so he went back in and stayed a while longer."
It was hardly a rager of a night for a young fellow, with his mum Dawn greeting him at the front door when he returned home about 1.45am.
He was happy as he embraced her in a big hug and planted a kiss on her head, wishing her a Happy New Year.
But he wasn't drunk. A toxicology report later showed there was a small amount of alcohol in his system — a reading of less than 0.05 — and caffeine, which puzzled investigators.
"The original toxicology (report) didn't show the level of caffeine, just that it was there, but the more thorough tests later discovered how much was in his system. It was a huge amount," Nigel said.
A Coroner's report received by the family last week showed Lachlan died of acute caffeine toxicity, after unknowingly ingesting a dangerous and fatal amount of it in pure powder form.
He mixed the powder with protein in a shake — something that many fitness enthusiasts do. It's a popular and widely available dietary supplement but just one teaspoon of pure caffeine powder is the equivalent of up to 50 cups of coffee.
"We know that Lach went off and had a shower, got into his pyjamas, turned his bed down and then made himself a shake," Nigel said.
Lachlan sent a Facebook group message to mates to say that the drink tasted awful and that he suspected the protein powder had gone off.
"He died not long after that, I'd say. He hadn't gotten into bed. He went to the bathroom because he felt sick. There was a small amount of vomit on the floor," Nigel said.
It likely that Lachlan suffered a heart attack. Nigel isn't sure — he hasn't been able to bring himself to read the full autopsy report.
"It was about 10am on New Year's morning and I was at my computer. Dawn got up and noticed his door was ajar. She peeked in and saw he wasn't there. She could see the bed hadn't been slept in. She suddenly got a really bad feeling," he said.
"She went to the bathroom and knocked on the door. There was no answer so she opened it and he was there.
"She called out and I went straight in. I put my hand on his back and he was cold as ice. I felt for a pulse but I knew there wouldn't be one. That was it. I went into a total state of shock."
For weeks, Nigel felt numb. He said everything reminded him of Lachlan — a beautiful bird or the swaying of trees in the breeze.
Grim things brought him to mind too, given how Nigel had found his beloved son.
Thoughts of having to call Lachlan's brother Martin, two years his senior, to share the horrific news also haunted him.
"I had to keep going," Nigel said.
"I couldn't stop. I started teaching again after a week and just threw myself into that. It was the best thing for me to keep busy.
"It was like my body went into self-preservation mode. I was in a numb state for a long while. Then it hit me like a ton of bricks."
Nigel penned a powerful Facebook post on Sunday that has since gone viral, warning of the dangers of pure caffeine powder, which is legal but unregulated.
News.com.au wrote about his public plea yesterday, sparking an outpouring of grief and concern.
"I don't think I intended on doing any of this," he said.
"The more I thought about it, the more I wondered if anyone else had this stuff. Maybe it was shared with other friends and they didn't know how potent it was.
"I don't know if he made many protein shakes. I don't think he was that into it. He was athletic and a good tennis player, he did a bit of fitness stuff — weights and push ups.
"He didn't know how potent it was. He wouldn't have kept it in the pantry if he did.
"This stuff is so dangerous and I worry that there are people who use it but have no idea.
"If the pure powder form could be banned from public sale, that would be a good step to change. It's way too dangerous."
Nigel doesn't want anyone else's child to suffer the same fate as his.
He doesn't want another young person's potential extinguished too soon, with entire lives of promise ahead of them.
"He was a very special young human being. He was much-loved, very generous in nature, always thinking of other people. He was very talented and extremely bright," he said.
"He had terrific potential for a really good career in whatever he chose to go into."
Lachlan was trying to decide whether to go travelling or pursue his love of science at university before he died.
"He had this beautiful picture of a galaxy on his wall. After he died, a friend named a star after Lachlan and it just happens to be one of the stars in that picture."