The EastEnders actress wished her other half a happy birthday alongside the snap, which saw them embracing in a poolside restaurant during one of their recent romantic breaks.
Thrilled with the sweet tribute, The Wanted singer reposted the photo and added the caption: “Thank you beautiful girl.”
The PDA-filled post comes after George made their relationship Instagram official on Sunday when he shared a heartwarming tribute to the 21-year-old on his story.
At the time, he was dating with Stacey Giggs, 43, but the couple split for good for a second time, which was revealed last month.
In August, George and Smith were first linked as they were pictured sitting next to each other on a flight to Crete, where an onlooker claimed that they were “all over each other”.
A passenger told The Sun: “They looked like a very loved-up couple - they were all over each other for the entire four-hour flight. Snogging and giggling like any new couple.”
Amid growing speculation about their romance, the singer took to his social media on Sunday (4 September) ahead of the actress’ Celebrity SAS: Who Dares Wins debut.
Showing his support, he shared a promotional shot of Smith from the new instalment and told his 337,000 followers: “You’re my winner already @maisiesmithofficial,” with a red heart emoji.
The soap star then reshared the post on her own Instagram story and placed an emoji of two hands creating a heart over it - marking the first time either of them have acknowledged their relationship on social media.
Smith, who played the role of Tiffany Butcher on the BBC soap, also tagged Max in her Instagram biography section, which she followed with a red heart emoji, in another nod to their budding romance.
His public show of support comes after the Glad You Came hitmaker reportedly confirmed that he had moved in with Smith during a tattoo session at INK’D in Fulham, London, where he got a large lion and rose tattoo on his forearm.
According to The Sun, George said: “She will just have to wait and see. I have shown a few designs and that but nothing, not that big. She likes tattoos, I’ve got a few already so it should be a nice surprise.
“I have wanted this for years, it’s not about anyone in particular, it’s not overly meaningful. It’s just the mix of the lion, I love lions and the rose, which matches the first tattoo I ever got.”
He added: “A guy showed me a design which I loved about ten years ago and I’ve just come down to London to spend a bit of time here and I thought you know what, change of scenery, get a new tat, new me, innit? Got my nails done.”