• A preview for This Is Us shows off Toby's weight loss.
• His wife, Kate, is shocked by his body transformation, since he's been working out in secret.
• And while the actor that plays Toby wears a fat suit for the role, he's also lost weight in real life.

Season 4 of This Is Us recently premiered, and as usual, the show has fans all in their feelings with its dramatic storyline. One storyline, however, promises drama of a different kind, as one character's shocking body transformation will cause some tension.

A preview for the newest episode of the NBC show features a shot of Toby's new body, and his wife—Chrissy Metz's Kate—reacts in surprise to his newly slimmed figure, as Toby has been working out and losing weight in secret.

Toby's weight has been a plot line since the show's beginning as the character meets Kate in a support group for overeaters, and he later has a heart attack that's related to his weight. Kate and Toby later have a child together, and the new baby leads Toby to get serious about his weight. But as the show's executive producer, Isaac Aptaker, revealed to Entertainment Weekly, Toby is actually being secretive about his weight loss goals for a very good reason.

"I don’t think he’s trying to flaunt in his wife’s face, 'Look at all the weight I’m losing,' especially given how busy she is with the baby and taking care of a newborn. So he’s made the choice of keeping this on the DL and flying under the radar here," Aptaker explained. "Certainly Kate is aware that he’s smaller, but she doesn’t know the extent he’s going to [in order] to lose the weight. And I think he’s doing that to try to protect her."

And while some fans have objected to the fact that Sullivan wears a fat suit on the show, the actor has actually gone through his own weight loss journey in real life.

During an appearance on Watch What Happens Live, Metz explained that, "Chris has been heavier and I think he does understand the plight of being overweight, and also he was the best man for the job."