“Happy 4th birthday our precious Rani Rose,” Hawn captioned the photo. “You are the real queen! I’ll take lady in waiting every day as long as the prince is always beside me! WE LOVE YOU!!!”

The couple’s costumes delighted their Instagram followers, with one commenter praising them as “the world’s best grandparents!!!”

Though they first met on the set of the 1968 Disney musical The One and Only, Genuine, Original Family Band — back when Russell was still in his teens — the actors didn’t become romantic until co-starring in Swing Shift, which started filming in 1983. By that time, both Hawn, now 76, and Russell, 71, were each divorced with kids. Nearly 40 years later, the Overboard stars’ modern family includes Hawn’s children Kate and Oliver (from her marriage to Bill Hudson), Russell’s son Boston (from his marriage to Season Hubley) and their shared 36-year-old son, The Falcon and the Winter Soldier actor Wyatt.

In 2020, the never-married stars told CBS’s Tracy Smith that there’s “no secret” to their romance.

“You both want to be together,” Hawn said. “You’ve got to want to be together.”

While it hasn’t always been smooth sailing over the decades, she added that “you can actually survive a relationship in a way that when you get older you go, ‘I’m so glad I got through whatever period that was.’ Relationships go through periods, sometimes really hard times. But there’s nothing sweeter than having a family, and that is worth everything.”

Playing dress-up isn’t the only way Hawn stays young. In a video shared this week by her oldest son, actor Oliver Hudson, the First Wives Club star can be seen enthusiastically bouncing away on a mini trampoline to Dua Lipa.

“She insists I came out of her belly but I’m not buying it,” Hudson quipped.