The 30-year-old singer and actress got engaged to her six-month old boyfriend Johnson ten days after Lachey announced his own engagement.
Lachey, who divorced Simpson in 2006, is set to marry his four-year-old girlfriend Vanessa Minnillo and Simpson wants to ensure that she ties the knot before him, Contactmusic reported.
"She wants to beat Nick to the altar. She knows that it is going to be tough to pull everything together on such short notice, so it might have to be a New Years wedding," said a source.
"In any case, she wants the focus to be on her wedding. She doesn't want her wedding to be the aftermath of his," the source added.
Simpson and Lachey, who starred together in the MTV reality show 'Newlyweds', got married in 2002 and split after three years.
The 'Blonde Ambition' star is making extensive plans for her December wedding."It will be big and elaborate. She'll spare no expense for fear that Nick and Vanessa will outdo her. She's already starting planning everything and has every family member working on her big day," said the source.
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