Jessica Simpson Joins Instagram: Poses With Engaged Couple Evan Ross And Ashlee Simpson; Shows Off Daughter Maxwell [PHOTOS]

Jessica Simpson, 33, is the latest celebrity to join popular photo-sharing site Instagram, sharing a black-and-white photo of herself and sister Ashlee, who is engaged to Evan Ross. In one photo caption, Simpson wrote: "It's official, I just joined Instagram before it's not cool anymore!"

Ashlee, 29, and Ross, 25, were engaged Jan. 13, after dating for about a year. "My baby love and I are ENGAGED!!! Hallelujah Hawaii!!!!!" Ashlee wrote after sharing a photo of the pair and showing off her new ring. Ross posted the same picture, but captioned it, “The love of my life said YES!” Evan, the son of Diana Ross, has had several acting roles and will be in “The Hunger Games: Mockingjay.”

This will be the second marriage for Ashlee Simpson, who has a 5-year-old son, Bronx, with ex-husband Pete Wentz. Jessica, who became engaged to former NFL player Eric Johnson in November 2010, is also set to eventually get married. "People ask me every day if I'm getting married. I'm like, 'I'm engaged, of course I'm getting married!'" she told People.

"He's put up with me and all my hormones for the two and a half years that I've been pregnant," she said. "He has seen me at my absolute worst but he hasn't gone far away." She previously shot down rumors that they would never walk down the aisle, saying, "I already feel like we're an old married couple already. Like, if he wanted to run, he could've run when I was hormonal and pregnant."

In addition to the family photo with younger sister Ashlee, Jessica posted an adorable picture of her daughter, Maxwell. The new mom, who gave birth to her second child, Ace, seven months ago, is looking more svelte than ever these days.

“As a mom I just have this confidence and I just feel so proud of what I’ve done and what I’ve accomplished," Simpson said. "And I really do also feel this need to just be the best role model for my children and I want Maxwell to look up to me and want to be like me. I don’t want to give her any false perception of what is real and what’s important.” Maxwell is her first child with Johnson.