On Saturday (17 January), viewers watched as JB came to support his cousin Marc Armstrong at the first audition stage of the BBC One talent show.
JB, who is currently in Austria training for the second series of The Jump, was seen cheering on Marc from backstage along with family and friends.
Marc performed John Lennon's classic 'Jealous Guy' in a bid to impress the coaches, but will.i.am, Rita Ora, Tom Jones and Ricky Wilson failed to turn around, meaning Marc didn't get through.
Taking to Twitter after Marc's audition aired, JB said: "Absolute liberty you didn't get through cuz @MarcArmstrongUK you have the talent of 10,000 and I always have your back x."
Absolute liberty you didn't get through cuz @MarcArmstrongUK you have the talent of 10,000 and I always have your back x— JB (@JBGill) January 17, 2015
Despite not progressing to the next round, Marc received positive feedback from the judges, who all told him not to give up on singing.
Rita said Marc was "really really good" and apologised for not turning.
Meanwhile, Tom declared: "I was almost there. I love the tone of your voice. Some of your phrasing was a little predictable in parts, but then again, thinking about it now afterwards I can straighten that out.
"You do have a really really good individal sounding voice and I'm sorry I didn't press the button."
Marc thanked fans for their support, writing on Instagram: "Once again thank you to everybody, the support has been overwhelming and I am so touched.
"It is such a surreal thing to be watching and listening to yourself on the TV! @bbcthevoice."
X Factor runner-up Fleur East, who is friends with JB, also tweeted her support for Marc. Fleur said: "@MarcArmstrongUK well done Mark!! Strong audition! Keep pushing, that talent can't go to waste!! Amazing voice! #thevoiceuk."
JB isn't the only famous face to pop up on this new series of The Voice UK, as Coronation Street actress and former Pop Idol star Kym Marsh supported her daughter Emilie Cunliffe, who unfortunately didn't get through to the next round.
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Watch Marc's audition below: