Kourtney Kardashian, who gave birth to son Mason Dash Disick yesterday in Los Angeles –coincidentally just one day after the fourth season premiere of Keeping Up With The Kardashians – ruined sister Kim’s chances of a Christmas marriage proposal from boyfriend Reggie Bush, according to an Australian tabloid report.

Word is when Reggie ran his idea for popping the question over the holiday season past the Kardashian clan, Kourtney hit the roof was having none of it.

“The Kardashian girls are best friends, but there’s tension because they are both attention hounds. Kourtney always wanted to be the center of attention, but for years Kim has been the queen bee of the family,” a spy spilled in the Dec. 14 issue of NW Magazine.

“She was furious and cried like a baby when Reggie told her he was about to propose. She screamed, ‘How can you do this to me? Kourtney feels like Reggie is purposefully sabotaging her special time by stealing the spotlight away from her. She doesn’t want anything to overshadow the birth of her son.”