MISSING soldier Sean Sargent is dead, most likely after crashing his car into the Brisbane River 18 years ago, a coroner says.

The 24 year old's disappearance has sparked rumours for years.

Did the soldier leave the army in 1999 to pursue a covert life with the French Foreign Legion?

Was he gay, living a secret life?

Did he commit suicide?

Coroner John Hutton said he had considered all these theories.

Mr Sargent's family watched from Mackay via video link as Mr Hutton delivered his findings on Wednesday morning.

"It is obvious…that Sean was much loved by his family and his friends," the coroner said.

Sargent had turned 24 two days before he went missing in March 1999.

He was last seen leaving his friend Benjamin Snelling's house in St Lucia.

Mr Hutton said the soldier would have driven away "under the heavy influence of alcohol, having consumed at least half a bottle of vodka."

The coroner said Mr Sargent most probably crashed on a blind turn, down a steep embankment without any road barriers.

"No-one would necessarily have been around, or heard it."

String tidal currents could have carried Mr Sargent and his car away, Brisbane Coroners Court heard.

Mr Hutton said he hoped the inquest might put to rest rumours, including those about Mr Sargent's sexuality, which were "of no consequence whatsoever".

He extended his condolences to Mr Sargent's family.

-NewsRegional