A spokesman for the Exeter and Greater Devon District Coroner's office confirmed there would be no inquest into the death of Gareth Jenkins, 25.
Lt Jenkins, from Colwyn Bay, Conwy, collapsed at the Commando Training Centre, Lympstone, Devon, while on a 30-mile (48km) march in May.
The former Eirias High School pupil played for Colwyn Bay Rugby Club.

It is under suspicion of meddling in the democratic process, of hacking computer systems and spreading disinformation with the alleged aim of helping a pro-Moscow candidate win the vote.
We heard such accusations this year in France and last year in America. Indeed, the US intelligence community has already concluded that Russia ran a campaign to influence the presidential election.
So, what about Britain's general election? Is the UK vote in the crosshairs of the Kremlin? Has it already been targeted by Russia's foreign intelligence service?
Last month UK Foreign Secretary Boris Johnson said there was a "realistic possibility" Russia might try to meddle. Has it? Does Moscow really care who wins the keys to Number 10?
I suspect not. In the run-up to the American and French presidential elections, it was clear that the Kremlin did have preferences.
The Russian state media was full of praise for candidates Donald Trump and Marine Le Pen, and scathing of candidates Hillary Clinton and Emmanuel Macron. Hardly surprising when you consider that both Mr Trump and Ms Le Pen promoted closer ties with Moscow.
But ahead of Britain's election, the Russian media hasn't come down on one side or the other. Indeed, there hasn't been much coverage at all of the campaign.
So why not?
"In Russia we don't see Great Britain as a fully independent country," says political analyst Sergei Markov, who is close to the Kremlin. "We see it as part of America: a very junior, junior partner of Washington."
In other words, in the eyes of the Kremlin, Britain is irrelevant.
Ouch, that hurts.
But that is only part of the story. Crucially, a UK vote has already given Russia the result it wanted - last year, when Britain voted to leave the EU.
Ahead of the UK referendum, the Kremlin officially remained neutral. But state media here were clearly backing Brexit.
Britain leaving was viewed as a body blow to the EU; that, in turn, was seen as a good thing for Russia, which has been on the receiving end of EU sanctions.
Welcome to the world of the zero-sum game.
But away from the corridors of power here, are ordinary Russians interested in the UK election? Do they even know that Britain is going to the polls?
To find out I drove to the town of Reutov on the edge of Moscow. It's twinned with Mansfield in Nottinghamshire.
There I chatted to the ballet teacher at the local youth centre, to a workman on the street, to young mums pushing their prams round the statue of Vladimir Lenin - founder of the Soviet state - and to pensioners on park benches.
Everyone I spoke to knew a great deal about Britain.
"It's the home of football", Ilya told me.
"Big Benâ€¦ the Queenâ€¦ Five o'clock Tea," said Ekaterina.
But of the people I spoke to, no-one knew that the UK was holding an election. Indeed, no-one could tell me the name of our current prime minister.
Perhaps that isn't so surprising when you consider that since the turn of the millennium the UK has gone through four prime ministers.
In Russia it's so much easier to remember who's in charge. After all, as president or prime minister, Vladimir Putin has been in power for more than 17 years.
A Royal Marines trainee who collapsed on a training exercise on Dartmoor died of natural causes.
[NEXT_CONCEPT]
These days, it feels like every time there is an election in Europe - or in America - Russia is cast in the role of bad guy.