But the 34-year-old showed off her post-baby figure this week and she looks amazing.
She and husband Tim Weatherspoon welcomed son Titan Jewell in November, and Kelly revealed she's working herself back into exercise.
Speaking at a Claritin event, the former Destiny's Child singer said: "I gained at least 70lbs!
"I'm in the process of [losing] it. My trainer Jeanette is really awesome, and we go through all these different routines.
"You know, we just have to get much more into the swing of everything now, especially because I like to change my workouts up so much. So I get a chance to be outside."
Gushing over Titan, Kelly said 'my baby boy is so delicious', and added that everybody thinks he looks like his dad.
She said: "I'm hoping that I get in there someone, because he does look just like her dad."
Kelly shared a picture from a recent magazine shoot this week, showing off her baby boy for the first time.