Jessica Simpson is little sis Ashlee's biggest fan.
"Roxie was all heart! Watching her up on that grandiose stage made me the proudest sister in the world. I love ya honey, I love ya!. Grrrrrrr," Jessica posted on Twitter after watching her sister's Broadway debut in Chicago Monday night. (Ashlee -- who recently finished a run on "Melrose Place" -- played the same role in the London production of "Chicago" last year.)
Jessica urged fans to buy tickets.
"Everyone in NewYork come tomorrow night and watch my sister at her best!!! I'll be there celebrating her return :)" she wrote on Twitter Sunday night.
She added, "I'm in NYC for my sis being Roxy in Chicago tomorrow night. I've looked forward to this moment since I watched her own the stage in London."