New mom Kourtney Kardashian has nixed Reggie Bush’s planned holiday wedding proposal to her younger sister Kim – because she doesn’t want to share the spotlight!

Kourtney – whose baby boy Mason Dash Disick arrived Dec. 14 – threw a fit when Kim’s football-playing beau tipped off the Kardashian family that he was planning to pop the question to Kim over the holidays.

"Kourtney screamed at Reggie, ‘You can’t do this to me!’" a family friend told The ENQUIRER.

"Kourtney is extremely hormonal right now, and her emotions got the best of her. Reggie was stunned and caught completely off-guard."

Although Kim’s mom Kris, stepdad Bruce Jenner and her other siblings were thrilled to hear about the proposal, Reggie was so unnerved by Kourtney that he decided to hold off, says the friend.

"Reggie doesn’t want to battle Kourtney, so he backed off to keep the peace.

"Now he’s planning on asking for Kim’s hand in marriage in early 2010, after Kourtney’s baby hubbub has died down."

Kourtney announced in August that she and Scott Disick – from whom she split at the beginning of the year – had rekindled their romance and were expecting a baby together.

"There’s always been underlying tension because Kourtney feels like she’s been playing second fiddle to Kim for so long," continued the source.

"She was hoping that the last days of her pregnancy and the first few weeks with her newborn would be all about her."

The fact that Scott has not yet proposed is also a sore spot for Kourtney.

Meanwhile, Kim and her New Orleans Saints boyfriend – who reunited in late September after breaking up two months earlier amid charges both of them were cheating – are house-hunting.

Kim put her Los Angeles condominium on the market, and Reggie agreed to sell his Hollywood Hills bachelor pad.

Despite Kim’s eagerness to move forward with Reggie, even she suggested putting their engagement off because she wants Kourtney to have her moment in the sun.

"Kim knows she and Reggie are in it for the long haul, so she’s OK with waiting," added the friend.