"Really sad about missing my 10-year high school reunion last night... so many people I wanted to see... but at least I have a good excuse," Cavallari captioned the snapshot.
Cavallari and Cutler were married in June 2013 and are also parents to 3-year-old son Camden and 19-month-old son Jax. The designer described the 32-year-old NFL star in an interview last year with Michigan Avenue magazine as a "very involved" dad.
"Jay is a great dad," she said. "He's incredibly hands-on, and he has been since day one. It's so sweet seeing him with Camden and Jax, and there's nothing sexier than seeing your husband as a great dad. I couldn't ask for a better partner in this situation."
Cavallari came to fame on MTV reality series Laguna Beach and went on to star on The Hills. She has since designed several fashion collections, including for Chinese Laundry, and will release the memoir/lifestyle book Balancing in Heels in 2016.