A Queensland grazier has left a multi-million-dollar bequest to the Royal Flying Doctor Service (RFDS) in what is believed to be one of the largest single donations made to the organisation in the state.

Geoffrey Carrick owned Maitland Station at Einasleigh in the far-north Queensland outback and died in June, aged 73.

The 138-square kilometre property was sold at auction for $9.85 million with the proceeds to be shared equally between the RFDS and the Children's Hospital Foundation.

Geoffrey Carrick would donate bullock horns for charity auctions. ( Supplied: Jon Rolley )

Mr Carrick's friend, Jon Rolley, said he was a "kind-hearted man" who gave generously to various causes, sometimes mounting bullock horns on timber plaques to be auctioned for charity.

"I think the last lot fetched over $4,000 and he'd give the money to the Mater Children's Hospital because he just loved kids," Mr Rolley said.

"He never had any of his own, he never married and he just liked to give to children."

Mr Rolley said Mr Carrick was modest about his donations and remembered once being at his place and noticing a photograph on the bench of a child with no hair and a breathing tube.

"I said to Geoffrey, 'Is that a relative or something?' and he said, 'Oh no, they just sent me that photo because I gave them a donation of $30,000 the other day'.

"Casual. Just gave away thousands and thousands of dollars to worthy causes that he liked to support and he never told anybody.

"He just did it because he's a kind-hearted man."

Mr Rolley said Mr Carrick was a true bushman who was brilliant with cattle, having honed his skills on his family's cattle property on Cape York Peninsula.

Geoffrey Carrick was remembered as a brilliant cattleman. ( Supplied: Jon Rolley )

"He knew more about cattle than most people have forgotten about cattle," he said.

"They were up on Strathgordon [Station] and it's isolated and the only chance you've got is the Flying Doctor up there.

"Geoffrey Carrick was a good man. I hope nobody forgets."

The Royal Flying Doctor Service Queensland said Mr Carrick's $4.925 million donation was one of the largest bequests it had ever received.

RFDS Queensland fundraising manager, Katherine Ash, said Mr Carrick first donated to the organisation in 2014.

"It was $50 and since then he donated a few times a year slowly giving bigger and bigger donations," she said.

"When we first heard that Geoffrey was going to be leaving a gift to the RFDS and the estate was coming we knew that it was going to be big but we had no idea how big.

"Everyone was pretty blown away."

It was a gift in a will that allowed the RFDS (then known as the Australian Inland Mission Aerial Medical Service) to lease its first plane 90 years ago.

Ms Ash said she hoped Mr Carrick's bequest would go towards the purchase of a new RFDS aircraft, which would cost almost $10 million and a further $2.5 million to fit out.

"Because our aircraft are operating 24/7, 365 days a year, we have to buy a new one every one to two years," she said.

"I'm hoping it will be based in one of our North Queensland bases so it will actually continue to fly over Maitland Station and watch over the community that he lived in."