"My first thought was something was wrong, you think 'has there been an accident?'," the ACT Brumbies coach said.

Instead Miller broke the news of his retirement from professional rugby union aged 27, trading football for life on the family dairy farm in Berry.

It comes as little surprise the unassuming Brumbies back-rower is happy to make a lowkey exit. Without a fuss Miller used to milk cows in the morning before making a two-hour trek to training and games, return home before the early wake-up to do it all again.

So when the Brumbies return for pre-season training next week as they look towards a Super Rugby AU season followed by a trans-Tasman competition, Miller will be living another dream.

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"It's his passion. He's been great for us in the period he has been at the club. You're disappointed because you lose a good footballer, but we're losing a great bloke who we've got a lot of time for," McKellar said.

"It genuinely interests me. They've got a beautiful property up there at Berry and they're really good people, I've been fortunate enough to meet his mum and his dad in the brief time he has been at the club. It's interesting, what they do there, and he clearly loves it.

"He's given professional footy a good crack, he was with the sevens, had a brief stint with the [Melbourne] Rebels, with the [NSW] Waratahs, and he has finished off here at the Brumbies.

"It would have been nice to get our hands on him four or five years ago, but we got him for a season and he certainly made an impact. He is a very popular member of our group. You lose a good footballer and a really good person."

Miller had the makings of another classic Brumbies success story, having made his way to the capital after being stuck behind Wallabies captain Michael Hooper in the pecking order for the Waratahs' No. 7 jersey.

He arrived in Canberra with little fanfare but quickly emerged as a key player in the club's charge to the Super Rugby AU crown, starting in the No. 7 jersey in the competition final against the Queensland Reds in September.

It is understood the Brumbies will leave a spot open on their roster in case they need to fill a void down the track, with McKellar already boasting plenty of options in the back-row before his players return for pre-season training on Monday.

"We've got good depth in the back-row. Jahrome Brown is back, Tom Cusack has got the ability to play seven and elsewhere in the back-row," McKellar said.

"It's a huge opportunity for those guys. There was always competition there between Will and Tommy, and Jahrome before he had to head back to New Zealand.

"It was incredibly competitive there and it will be no different next year."