Danny, 27, announced the happy news on Twitter on Thursday night, writing, "The future mrs j yeahhhhhh!!" He posted a closeup picture of the delighted couple smiling for the camera, with Georgia holding up her hand to show off her new diamond ring.
Shortly afterwards the former beauty queen, 26, posted the same picture on her page, excitedly writing, "Soooo this happened tonight!! I'M ENGAGED!!!! So so happy!!!"
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Danny will be the third member of McFly to tie the knot. His bandmate Tom Fletcher was the first to walk down the aisle in May 2012 when he married Giorgina Falcone, the sister of TOWIE's Mario Falcone.
The reality star was among the first to congratulate Danny and Georgia — "Congratulations @Dannymcfly @GeorgiaHorsley1 on your engagement!!! Well done mate x."
Strictly Come Dancing champion Harry Judd was the second member of the band to marry, when he exchanged vows with Izzy Johnston in December 2012.
Bride-to-be Georgia is a former beauty queen who was crowned Miss England in 2007. She started dating Danny in late 2009, shortly after he split from her Miss England successor Laura Coleman.
Just last year, Danny admitted that he wasn't ready for marriage in an interview with the Daily Mirror. "It's serious," he said of the relationship. "But I don't think I'm quite at the putting-a-ring-on-her-finger stage. Maybe in a couple of years.
"Girls still ask me out and I'm like, 'No, I've got a girlfriend'. I've done my bit for the boys and it was great while it lasted. But I'm well and truly over that now."