IN a blockbuster world ex­clusive, The ENQUIRER can reveal that police believe “Blade Runner” OSCAR PISTORIUS killed his stunning girlfriend in a fit of rage after she told him she was pregnant!

What was supposed to be a ro­mantic Valentine’s Day for the couple at the Olympic hero’s South African mansion exploded into a deadly rampage when she broke the baby news to Oscar – shortly after he’d flown into a jealous rage over suspicions that she was cheating on him.

“Police believe the preg­nancy secret she revealed is what sent Pistorius over the edge and left her dead, with bullet wounds to the head, chest, pelvis and hand,” an insider close to investigation told The ENQUIRER.

Pistorius, 26, and Reeva Steen­kamp, 29, a gorgeous law school graduate and model, had been dat­ing since they met at a party three months ago. He was an Olympic icon and she a beauty set to appear in a reality TV series, so it didn’t take long for them to become known as South Africa’s golden couple.

No one suspected trouble in para­dise when a local TV crew filmed Reeva arriving at the runner’s posh Pretoria home at 6 p.m. on Feb. 13 – just hours before the bloodbath.

“Later that night, neighbors com­plained of shouting and fighting coming from the house,” said the source. “Police were called to in­vestigate, but it appeared to be just another lover’s spat, so nothing was done except to ask them to quiet down.”

The couple soon went to bed, according to authori­ties, and Pistorius’ mansion turned into a House of Death at about 3 a.m. on Feb. 14.

“Police theorize that Pisto­rius was in a rage – possibly induced by the illegal steroids that were later recovered in his home – and bludgeoned Reeva with a cricket bat during a fierce argument,” said the source. “When police found the bat, there was lots of blood on it.

“Investigators believe Pistorius shot the young woman once while they were fighting.”

Terrified and bleeding heavily, Reeva somehow managed to get into the adjoining bathroom and shut the door before her enraged boyfriend fired three more shots from his Tau­rus 9 mm pistol through the door – snuffing out her life.

But even before that, Pisto­rius – who made history by running in the London Olympics last summer wearing prosthetic carbon-fiber blades – was already said to be seething with jealousy.

“Police believe the argument started over Reeva’s relationship with Oscar’s close friend, handsome rugby player Francois Hougaard,” said the source.

“Oscar discovered that Reeva and Francois had been texting each oth­er, and police later found evidence of their communications on Reeva’s iPad.

“Those e-mails were the opening salvo in the fight that got out of hand and led to murder.

“Police believe as the arguing con­tinued, hot-headed Pistorius became mani­acal. Reeva tried to calm him down, saying there was nothing between Hou­gaard and herself. Although she had dated him in the past, it was long over.”

But the Blade Runner continued to vent, and desperate Reeva blurt­ed out that she was pregnant with  his child, investigators believe. Instead of soothing him, cops think that the baby revelation incensed Pistorius even more and he screamed that the baby wasn’t his before launching his deadly attack.

Hearing the commotion at the house, alarmed neighbors alert­ed security at the heavily guarded Silver Woods Country Estates, the gat­ed community where Pistorius lived and residents are protected by 10-foot-high walls.

Realizing what he’d done, the fright­ened athlete apparently carried his girlfriend’s blood-soaked body from the bathroom and tried to revive her.

The security guards were con­vinced Reeva was clinging to life as Pistorius desperately tried giving her mouth-to-mouth resuscitation, but she died soon after.

Later, the disgraced Olympian claimed he had thought there was a burglar in the house and the shooting was a horrible mistake.

“But that doesn’t make sense,” the insider said. “Reeva had been in the house since 6 p.m. the day before – and he knew she was there. Police aren’t buying that story either and have charged him with premeditated murder.”

The Blade Runner’s dark, danger­ous side – including his fascination with guns – is well-known to previous girlfriends. In fact, at the time of the shooting, a source says Pistorius was applying for seven gun permits, in­cluding one for a machine gun.

Marketing student and part-time model Samantha Taylor, who dated him last year, said Pistorius is “certain­ly not what people think he is.”

And her concerned mom Trish de­clared: “I’m so glad that Sammy is safe and sound and out of the clutches of that man. There were a few occasions where things could have gone wrong with her and his gun during the time they dated.”

Once, Samantha was at a celebrity event at a South African racetrack with coal mining millionaire Quinton van der Burgh when they were confronted by a jealous Pistorius, according to an­other source.

“Oscar was rabid with anger,” recalled the source. “Later he sent e-mails to van der Burgh, threatening to break his legs. He was initially ar­rested for the threats but later released.”

Samantha calls Pis­torius the “ultimate player,” meaning he is a cheater – and sources say he was two-timing her with a Russian model.

In September 2009, the short-fused athlete spent 17 hours in jail after being charged with common as­sault against college student Cassidy Taylor-Memmory. She alleged he had aggressively slammed a wooden door on her, injuring her leg, after they fought during a party at his house.

Earlier in 2009, Pistorius was admitted to the hospital with serious facial injuries following a speedboat ac­cident. It was reported at the time that police had found empty booze bottles on the boat, but his blood was never tested.

Said the source: “Oscar was a lot more screwed up than anyone realized at the time!”