Anstead and Zellweger have been linked romantically since June 2021.
"Happy birthday To this beautiful lady," Anstead wrote alongside a selfie of the two embracing each other on his Instagram Stories. "Ren you are PURE CLASS."
The U.K. native went on to add, "I know how lucky I am."
Anstead's post came just two days after he shared a throwback image of himself with Zellweger from the set of Celebrity IOU: Joy Ride, where the two first met.
"WOW! This just popped up in memories," he wrote. "One year ago today! Sat on the back of a fire engine on the final day of filming having handed two amazing men a car as a thank you from Ren. Amazing what can happen in just one year……."
Anstead and Zellweger were first romantically linked in June 2021, right around the same time his divorce from Christina Haack was finalized. (Anstead and Haack -- who share 2-year-old son Hudson --wed in 2018 and announced their separation in 2020.)
By that August, Anstead posted his first Instagram photo with Zellweger.
"It’s finally here…. The first episode of #CelebrityIOUjoyride is available on @discoveryplus Monday the 23rd!! And it’s the incredibly magical Renee Zellweger," he wrote. "Join @cristylee09 Ren and me as we pay it forward to two amazing men that gave so much to one of Ren’s dearest and closest friends……Xx."
That same month, Anstead co-hosted ET and reflected on the unexpected timing of their romance.
"Sometimes things come to you at the right time, and actually the right time is often the most unexpected," Anstead shared. "There's absolutely no way it was something I expected, but there's something magical in that right?"
The Judy actress spoke about how her time on Celebrity IOU: Joy Ride with Anstead was inspired by her late friend and publicist Nanci Ryder, who died in June 2020 after a battle with ALS. Zellweger went on the show to gift cars to two nurses who cared for Ryder and she believes her late friend may have been the magic behind her meeting Anstead.
"Yeah, we do joke about that,” Zellweger shared. “She’s always doing her best. It made me smile. It made me smile to think on this, yeah, the serendipity of it all."