JB posted the snap on Instagram earlier today (3 September) and shared it with his fans on Twitter. He said: "Caught napping!! @marvinhumes haaaa J x."
The star then joked that Marvin's tiredness was down to the fact that he's a first-time dad to baby daughter Alaia-May!
When a fan asked why Marvin was always napping, JB joked: "He's a father now, getting old! x."
Marvin, who welcomed Alaia-May into the world with wife Rochelle on 20 May, appeared to be sleeping peacefully as he slumped his head against cream sofa chairs. Meanwhile, JB pulled a funny open-mouthed expression at the side of the photo.
We don't think Marvin will let this one slide though. As soon as he saw the photo, he replied: "@JBGill liberty..ok ok..baited on Twitter..your turn is next secret squirrel..I'm coming for you."
Let the boy band banter commence!
Last week, the group - JB, Marvin, Oritsé Williams and Aston Merrygold - filmed their last ever music video, which will wrap up their six-year music career before they split at the end of the year.
That hasn't stopped them from singing to fans up and down the country though, and this weekend the group headed to Birmingham to perform at Fusion Festival.
They sang a medley of their chart-topping hits but were a man down as Oritsé was busy taking part in ITV celebrity dance competition Stepping Out, alongside his girlfriend AJ Azari.
Check out JLS' best moments in pictures:
Copyright: WENN ITV