The French Foreign Legion is one of the most mythologised fighting units in the world. Now, their newest recruit could be a 21-year-old construction worker from Wallan.

Missing man Dean Ranieri​ has been found alive after vanishing for four weeks while travelling on his first overseas trip to Europe.

No one had heard from him since he posted on his Facebook page on May 18. He left on a flight for France on May 14.

His worried mother, Louisa Fantauzzo​, said she wept "happy tears" when the Australian consulate rang her to say that French police had found her son safe and healthy.

She believed Mr Ranieri had followed his dream to sign up to the French Foreign Legion, after he was knocked back from joining the Australian military.

"He's always wanted to be in the army, he's always trained for it," she said on Tuesday.

"But I just didn't believe he would go and do it. But he's followed his heart and dream and I am proud of him."

Ms Fantauzzo said her son had talked about joining the Légion étrangère with his sister and had been committed to serving in the army his entire life.

"He's a pretty strong-headed person," she said.

"He's fighting for all of us, the whole world. That's what they are, the French Foreign Legion."

Famous for its caped kepi hats and accepting soldiers from all corners of the world, the Foreign Legion was formed in 1831 to protect France's colonial interests.

It has a reputation, particularly in popular culture, of being the place of last resort for criminals looking for a new start. However, recruits nowadays are subject to more stringent background tests.

With an initial contract of five years, Legionnaires are paid and receive free food and accommodation.

They are also entitled to French citizenship after three years, which will be granted even faster for wounded soldiers under the provision of Français par le sang versé (French by spilled blood).

Recruits must pass a series of physical and psychiatric tests, according to foreignlegion.info, and are only allowed to contact their family by mail and payphone after starting basic training.

To enlist, recruits must sign up on the French mainland, with the selection process taking between two and five weeks. Recruits do not need to know French when they join.

Ms Fantauzzo said she didn't know her son planned to join the Legionnaires on this trip but looking back there were some hints.

"When I left him at the airport, he had tears in his eyes," she said.

"The family are all so relieved, they're just all proud of him, that he's followed his heart. We're so glad he's alive, not dead."

If given the chance to talk to her son, Ms Fantauzzo said she would tell him that he should have let her know what he was up to before bidding adieu.

But she would also say say how happy she is for him that he has pursued his dream to join the military.

"I'd tell him 'I'm proud of you, what you've done and followed your heart and that you're safe and happy'," she said.