The snaps showed Parker's birth date - 4 August 1988 - etched onto the top of George's chest.
He also had it done on Parker's birthday, the day he would have turned 34.
"04.08.1988," wrote the star, along with a heart emoji. "Happy Birthday brother… You’re always with me."
Parker told fans in 2020 that he had been diagnosed with inoperable stage-four glioblastoma while his wife Kelsey was expecting their second baby.
He passed away in March and George, 33, acted as one of the pallbearers at his funeral alongside their bandmates Siva Kaneswaran, Jay McGuiness and Nathan Sykes.
In June, George said he "hasn't yet processed" the loss.
Appearing on Loose Women, he said: "It’s been a strange couple of months. I’ve just been doing stuff constantly."
He added: "With [Tom] passing and being there, doing a TV show, then the funeral, it’s been… I’ve not really processed it yet."
Kelsey, who has three-year-old daughter Aurelia and son Bodhi, one, with Parker, also paid tribute to her late husband on his birthday.
Sharing a video clip on Instagram of her on a train with family and friends, she told fans: "Not going to lie, it started as a really tough day, feeling pretty fed up with the world but thankfully this lovely lot have lifted my spirits...
"@k2kstars trip to see 101 Dalmatian’s at Regent's Park, how can their voices not fill you with a bit of joy.
"Happy Birthday up there my love, miss you more and more each day.
"I know you will be proud of me and your babies."
Watch: Kelsey Parker on Tom's legacy, The Wanted reforming and how the band have supported her