Ashlee Simpson attends the American Ballet Theatre opening night Spring Gala at Lincoln Center on May 13, 2013 in New York City. Credit: Stephen Lovekin/Getty Images

Is Ashlee Simpson trying to steal the fashion spotlight from sister Jessica? The 28-year-old singer looked jaw-droppingly gorgeous at the 2013 American Ballet Theatre Opening Night Spring Gala at NYC's Lincoln Center on Monday, May 13.

Simpson showed off her stunning figure in a black backless gown by Alice + Olivia. The lace design featured a feathered peplum accent at the waist, and she accessorized the glamorous look with emerald green Nualah earrings by Ocnarf Sairutsa and a metallic clutch.

On Sunday, the busy mom showed off a gift she received from 4-year-old son Bronx for Mother's Day on Twitter. The single star, who split from Boardwalk Empire actor Vincent Piazza in November 2012, posted a picture of a beautiful bouquet of flowers that included the note, "Happy Mother's Day! Love always, Bronx."

Perhaps her ex-husband, Pete Wentz, helped their son send the gift? The 33-year-old Fall Out Boy bassist recently praised Simpson for her mothering skills.

"I feel like we both realize that we're parents and we're in it for our kid. That's made it really easy," Wentz said on an Apr. 15 episode of Watch What Happens Live. "I feel like, as a mom, she's awesome. She's an awesome mom and we get along really well when it comes to our kid now."

Tell Us: What do you think of Simpson's backless American Ballet Theatre Spring Gala gown?