updated 01/15/2014 AT 3:45 PM ET
•originally published 01/15/2014 AT 5:00 PM ET
“Family moment,” she captioned the picture, which shows Ashlee’s one-of-a-kind engagement ring, a five-carat sparkler custom-designed by jeweler Neil Lane.
Ross, 25, popped the question while the two vacationed in Hawaii, sharing the news with his own celebratory Instagram. From Jessica’s photo, it seems Diana Ross’s son has earned the Simpson family’s approval.
It’s unclear which sister will take their second trip down the aisle first – both Simpsons were also previously married, Jessica to Nick Lachey and Ashlee to rocker Pete Wentz, the father of her 5-year-old son, Bronx Mowgli.