Clint Eastwood has taken an unconventional move with his latest film, tapping the heroes of the 2015 Paris train attack to play themselves in their own biopic.

The 87-year-old director has cast Anthony Sadler, Alek Skarlatos and Spencer Stone to recreate the dramatic moment they tacked an AK-wielding gunman.

Eastwood and the studio had already completed casting for the film, titled The 15:17 to Paris, when the unusual decision was made at the last hour, Variety reported.

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Director Clint Eastwood (right) presents a Heroes Award to (l-r) Anthony Sadler, Specialist Alek Skarlatos and Airman First Class Spencer Stone at the Guy's Choice Awards in 2016

In August 2015, all three men disarmed and subdued Ayoub El Khazzani (pictured), who was armed with an AKM rifle and a box cutter, aboard a train from Amsterdam to Paris

The film recreates the dramatic moment the three men tackled Moroccan terrorist Ayoub El Khazzani, 25, who had boarded the train from Amsterdam to Paris.

While sources say the men will have 'good-sized roles', the film - based on their book of the same name - also flashes back to their time growing up together in Sacramento, California.

That means they will share the dramatic weight with other actors; Paul-Mikel Williams, Max Ivutin and Bryce Gheisa, will play childhood versions of the three; Cole Eichenberger, and William Jennings will play older versions.

Eastwood himself met all three men at Spike TV's Guy's Choice awards in June last year, where he presented them with the Heroes Award.

Stone, Skarlatos and Sadler rose to prominence when they tackled Khazzani, who boarded the train on August 21, 2015, hiding an AKM - an updated version of the AK-47 rifle.

Stone, then a 23-year-old airman, was travelling with 22-year-old Oregon National Guard member Skarlatos, who was on leave after a tour of Afghanistan.

They had been joined by their friend Sadler, 22; all three men were travelling to Paris and had just crossed the French border when Khazzani emerged from a toilet and started firing.

The three heroes (pictured) became famous after the incident; Stone was injured by the terrorist, almost losing his thumb to the man's box cutter, but tended to others in the aftermath

Khazzani was heavily armed with multiple magazines (left; right, police investigating afterward) in the attack. The men were awarded in both France and America for their bravery

Stone (pictured leaving hospital after the train incident) was later stabbed outside a Sacramento nightclub defending a female friend; he had emergency surgery but survived

Speaking shortly after the attack, Sadler said: 'We heard a gunshot, and we heard glass breaking behind us, and saw a train employee sprint past us down the aisle.'

'As he was cocking it to shoot it, Alek just yells, "Spencer, go!" And Spencer runs down the aisle.

'Spencer makes first contact, he tackles the guy, Alek wrestles gun away from him, and the gunman pulls out a box cutter and slices Spencer a few times. And the three of us beat him until he was unconscious.'

In another account, Skarlatos said he yelled 'let's go'.

Also involved in the incident were British businessman Chris Norman, 62, French-American Mark Mooligan, 51, an off-duty train driver who did not wish to be identified and a 28-year-old French banker identified only as 'Damien A.'

In the melee Stone was stabbed several times - almost severing his thumb - and Mooligan was shot in the throat.

Despite his injuries, Stone turned to help Mooligan once Khazzani was subdued. Mooligan survived after being operated on in hospital.

Skarlatos, Stone and Sadler were awarded top Marine, Air Force and civilian honors by Barack Obama, and they were also made knights in France's Legion of Honor

The men also became celebrities; Skarlatos (seen being awarded the Soldier's Medal for his bravery, left) also appeared on Dancing With the Stars Live! (right)

The heroism of the three Americans led to them becoming minor celebrities.

They were inducted as knights in the French Legion of Honor, and upon returning to America they were declared 'Sacramento Hometown Heroes' in a parade held for them.

President Barack Obama also awarded the men a series of medals in a special event at the Pentagon.

Stone received the Airman's Medal and Purple Heart; Skarlatos received the Soldier's Medal, and Sadler was given the Secretary of Defense Medal for Valor.

Stone was also promoted to senior airman and then, shortly afterward, staff sergeant.

Skalartos also appeared on the Dancing With the Stars Live! Dance All Night Tour in 2016.

Eastwood, 87, decided to cast the three men in his upcoming film at the last minute, after casting had already concluded. His choice to not rely on big stars mirrors 2008's Gran Torino

The heroes don't have to do all the heavy lifting, however - (l-r) Paul-Mikel Williams, Max Ivutin and Bryce Gheisa have all been cast as the men for childhood scenes

Stone suffered again in October 2015, when he was knifed outside a nightclub in Sacramento by James Tran, 28.

Stone had been defending a female friend who had been recorded on a cell phone by a member of Tran's group, police said.

The badly injured veteran underwent open-heart surgery due to injuries to his heart, lungs and liver, but ultimately recovered.

Tran pleaded guilty in May and received nine years in prison.

The 15:17 to Paris will be Eastwood's fifth biopic in a row after J Edgar, Jersey Boys, American Sniper and Sully, and his latest to rely on a largely unknown cast since 2008's Gran Torino.

It is based on the autobiography by Sadler, Skarlatos, Stone and Jeffrey E Stern.