The former "Scrubs" star has been romancing the British star since August 2018, and couldn't resist celebrating her big day with a glowing social media tribute, in which he called her the "most fun person" he's ever met.
"Happy Birthday to the most fun person I've ever met. I would have felt blessed to have smiled with your for one night. I can't believe I get to giggle with you everyday (sic). What a pleasure it is to know you. What a gift to the world it was that you were born," he wrote.
The "Midsommar" star then shared Zach's post on her own Instagram Story and responded with a single red heart emoji.
Meanwhile, the sweet post comes after Florence previously defended the 21-year age gap between herself and her boyfriend.
Speaking last July (20), she said, "I've always found it funny, how I can be good enough for people to watch my work and support my work and pay for tickets and I'm old enough to be an adult and pay taxes but I'm not old enough to know who I should and should not have sex with."
"Once again making a young woman feel like s**t for no reason."