MARIE OSMOND has been rocked by a shocking family sex scandal that triggered her 23-year-old daughter Rachael’s rush to the altar on Christmas Day!

The ENQUIRER has learned the real reason why Rachael had a quick­ie wedding in a Park City, Utah, cabin only 10 days after her fiance Ga­briel Krueger proposed.

“They rushed to get mar­ried at warp speed be­cause they wanted to start having sex,” revealed a family insider.

“But the quickie wed­ding caused a rift between Marie and her daughter. She thought Rachael should wait until November so she could have a proper ceremony in a Mormon temple.

“But Rachael didn't want to wait – she wanted her lovemaking with Gabriel to start now. And in the Mormon religion, sex before mar­riage is not allowed.”

Headstrong Rachael “is driving Marie crazy and had her in tears,” a source close to the family told The ENQUIRER.

Rachael’s 22-year-old fiance is a recent Mormon convert, but under tenets of the church, converts must be members of the church in good standing for at least a year before they can be wed in a Mormon temple.

“Marie had to go along with the couple’s wishes because they made it clear they didn’t intend to wait a whole year to have sex,” said the close source.

Rachael, who works for her mother as a wardrobe stylist, met Gabriel, a student at the Illinois Institute of Art, in December 2011 when she was in Chicago working on the “Donny & Marie” holiday show.

The following February, Rachael invited Gabriel on the “Donny & Marie Cruisin’ with Friends” cruise from Fort Lauderdale to Nassau – and Marie rocked the boat with a startling announcement.

“Marie introduced her daugh­ter from the stage as Rachael Blosil Krueger and told everyone they were planning to marry,” a source on the ship told The ENQUIRER.

But then, on June 11, Marie made another surprise announcement via Twitter, saying that Rachael was now engaged to Las Vegas emergency medical technician Bart Ritchie. That relationship wound up fizzling a few weeks later, and Rachael soon ran back into the arms of Gabriel.

The romance heated up so much that in December Rachael told her 53-year-old mom she was hot to trot down the aisle with Gabriel, even if it meant no church wedding.

Deeply religious Marie “hit the roof,” revealed a family insider. “Rachael’s decision caused Marie a huge amount of embarrassment, in part because a lot of people will mistakenly assume that the wed­ding happened so quickly because Rachael is pregnant.”

But Rachael has done her best to soothe her mom’s temper.

“Rachael promised Marie that as soon as they are able to have their mar­riage sealed in a Mormon temple, they will,” said the close source. “And in the end, Marie accepted it – although reluctantly.”