Kerry, 34, and Brian, 35, share daughters Molly, 13, and 12-year-old Lilly-Sue, and the former Westlife singer acknowledged their new stepdad with a heartwarming post.
He wrote: "Happy Father's Day @mrgsjkay thanks for keeping our family together! Your a great man [sic]."
George was quick to respond to Brian, writing: "@BrianMcFadden happy father's Day buddy.. It's a joint effort.. The girls are lucky to have 2 good men they can call dad. See you soon pal x [sic]."
Even Kerry joined on the PDA, tweeting to Brian: "Same to you too love x [sic]."
Atomic Kitten star Kerry and Brian split in 2004, and have been publicly feuding on and off ever since, but their mushy messages of affection suggest that they're getting on these days for the sake of the children.
Kerry is also mum to Heidi, eight, and seven-year-old Max from her marriage to Mark Croft, and she and George share daughter Dylan-Jorge Rose, one.
It's lovely to see Kerry, George and Brian getting along, isn't it?