The foursome have reunited to represent the UK at next month's competition. In an upcoming BBC documentary, various stars throw their support behind Duncan James, Lee Ryan, Simon Webbe and Anthony Costa.
"I think Blue are gonna do really, really well," Take That star Williams says. "They've got as good a shout as anybody. Good luck, bring it home!"
JLS' Marvin Humes adds: "Biggest wishes to Blue, best of luck. I used to play for my football team when I was 11 or 12 and it was the year that Katrina won Eurovision with 'Love Shine A Light'. On the Sunday when we won a game, for some reason, that was the song we were singing when we were warming up."
Meanwhile, Lulu raves: "I think Blue are brilliant, they will be great ambassadors."
The group, who are the bookies' second favourite to win the contest, unveiled the official music video for the single yesterday.
> Phillip Schofield "honest" with Blue criticism
Watch a preview from Eurovision: Your Country Needs Blue below:
Eurovision: Your Country Needs Blue airs tomorrow at 6.10pm on BBC One.