Moore, who played matriarch Rebecca Pearson, looked back on the early days of This Is Us, right when the series took the TV world by storm.
"[Six] years ago today, #thisisus premiered. It feels like yesterday and also a million years ago. So grateful to all of you who came on the ride with us and let us tell this incredible story," Moore wrote on Instagram with a series of photos. "Here a few snaps from those first few crazy months (slide 2 was our premiere party at some random sports bar where we all live tweeted the show lol). Missing my Pearson fam a lot today!"
Metz and several of Moore's co-stars left heartfelt comments reminiscing on This Is Us' first year, with Metz writing, "What a time. Heartstrings officially pulled."
Brown and Watson, who played married couple Randall and Beth (or "R&B," as they're more affectionately referred to), wrote a joint message to the fans on Twitter and Instagram, sharing loving photos of the pair from the show.
"September 20, 2016. One for the books. The start of R&B," they wrote, adding a red heart emoji. "Tag the R to your B…or the B to your R. We celebrating love y’all!!!"
Metz, meanwhile, asked fans to share their favorite memories from the show as she reflected on playing Kate.
"You first met the Pearson family 6 years ago today… our forever fam," the actress wrote. "Happy premiere anniversary, #ThisIsUs 💛 Share some of your favorite @nbcthisisus memories below to celebrate."
It was a blast from the past for Sullivan, who played Toby, as he shared never-before-seen on-set photos of the cast over the years.
"Wow. #ThisIsUs premiered 6 years ago today?!?? Crazy. Even crazier is all the fun we had taking pics with our prop phones…for the first time ever…please enjoy!" the actor captioned his series of photos.
This Is Us ended its run on May 24 after six seasons and 106 episodes and became part of the pop-culture zeitgeist. After the series finale, Fogelman explained why he wasn't interested in continuing the story any further -- at least for now.
"I'm pretty set on this being it. Outside of understandable questions about Audio the Dog, for the most part, we really answered the questions of the show," Fogelman told ET on a conference call with reporters back in May.
"My well is pretty dry right now and I think we wanted to end the show when we thought we were at our creative strong point before it got too tiring, too hard for us to come up with ways to keep it special and interesting. I feel this is the right endpoint," he acknowledged. "Who knows what change of heart or midlife crisis brings but I feel like we've put these stories to bed now. Certainly for quite a bit of them."
For now, we'll have these This Is Us memories to look back on.