Credit: Jeff Vespa/

Jessica Simpson famously came to younger sister Ashlee's defense, calling Melrose Place "crap" after her sib was canned.

Now she is serving as cheerleader as Ashlee signs on for a new job, playing Roxie Hart in Chicago on Broadway. (Ashlee, who has already dyed her hair black, made her London stage debut as Hart in the West End production of Chicago in 2006.)

"Just finished second CHICAGO rehearsal," Ashlee, 25, Twittered. "Man I love the theater and putting my dancing shoes back on!!"

Jessica, 29, then responded, "All that jazz:)"

A short time later, she was still excited about her sister's new gig.

"I can't wait to watch @ashsimpsonwentz on broadway in all of her glory!!!" Jessica Twittered. "I get chillbumps from toes to noggin thinking about it!!! YAY!!!!!"

While Ashlee readies to take the stage, Jessica -- whose weight was widely scrutinized this year -- has been hitting the gym.

"Just got done boxing and I can barely type!" she Twittered. "If anyone sees me puking on coldwater canyon starting singing the Rocky theme song :)"

She previously complained (via Twitter) to trainer Mike Alexander that his workouts were leaving her with "a pouty face and sore buns."

But Alexander Twittered back that he wasn't worried about the singer. He called her a "badass" whose "efforts know no limitation."