It’s an all-out battle between LISA MARIE PRESLEY and wild-child daughter RILEY, 22, over her surprise engagement to “I am Number Four” Brit hunk ALEX PETTFYER.

Four-times-wed Lisa Marie – who’s desperately trying to stop her daugh­ter from following in her disastrous marital footsteps – is vowing to block the wedding, convinced that Pettyfer, known to have a bad temper and a vulgar mouth, is just after the Presley fortune, say sources.

“Lisa Marie doesn’t believe this marriage has a chance in hell of lasting,” declared a close source.

“Riley has horrible taste in men. She’s dated womanizing pop star Ryan Cabrera and a number of irrespon­sible, pretty-boy male model-types. Lisa Ma­rie thinks her daughter is far too young and impressionable to un­derstand what she’s getting in to.

“She’s worried that Alex just wants to sink his hands into the Pre­sley family fortune,” estimated at more than $300 million.

To complicate matters more, Alex, 21, who starred in the sci-fi thriller “I Am Number Four,” and Riley are both tied up with their careers. She has four movies coming out in 2012 alone.

Despite the furious protests of her 44-year-old mom – whose bizarre marriage to Michael Jackson lasted less than two years – lovestruck Riley is standing her ground.

“The engagement news is ripping the Presley family apart,” divulged an insider. “Riley is ready to go forward – with or without mom’s blessing.

“Worse yet, Riley has been tell­ing friends she wants Alex’s baby, and she’s been hinting she’s already pregnant. That would be Lisa Marie’s worst nightmare.”

After just six months of dating, Elvis’ granddaughter got engaged to Alex, who co-starred with her in the movie “Magic Mike.’” Pettyfer plays a male stripper, Riley his exotic dancer lover.

Following the revelation they’ll soon walk down the aisle, a thrilled Alex tweeted: “I’m very happy in my per­sonal life.”

On March 12th, a radiant Riley was spotted in Los Angeles sporting a gleaming diamond engage­ment ring when she and Alex went on a lunch date.

But despite his ro­mantic charm, Alex has a dark past, say sources.

He and former girl­friend Dianna Agron split after a year, and she reportedly went into hiding  after the nasty breakup because she was so scared of his temper.

 “Lisa Marie doesn’t trust Alex,” divulged the close source. “She thinks he’s bad news – young and immature and too much of a playboy charmer.

“She will do anything to prevent Riley from enduring the heartache she has suffered. But the more she objects to the nuptials, the more Riley seems determined to marry Alex.”