The actress/singer was so focused on fine-tuning her acting skills, she missed out on gym visits, and quickly realised she needed to get back into shape as filming began.

"I'm in serious actress mode right now," she revealed to Entertainment Tonight. "I haven't been working out as much while I've been doing the series, so I feel a tiny bit out of shape right now, but that's OK."

As Shades of Blue debuts in America next month (Jan15), Jennifer will be in rehearsals for her first residency in Las Vegas. The show, titled All I Have, kicks off at Planet Hollywood's AXIS theatre on 20 January (15), and she promises fans she'll be in tip-top shape by then.

"I know it in my mind, because I'm like, 'OK, now you're going to start dancing eight, nine hours a day and it's going to be a whole different story'. And we'll tighten it up right quick."