Kelly Clarkson in awe of Chrissy Teigen's post-pregnancy slim down

Kelly Clarkson is in disbelief at how quickly her fellow new mum Chrissy Teigen has regained her slim figure.

The Because of You hitmaker welcomed her second child, son Remington, on 12 April (16), four days before model Chrissy and her husband, John Legend, became first-time parents to daughter Luna.

Now, just three weeks on, Chrissy appears to have already shed most of her excess baby weight after John showed off a snap of his wife cooking a Mother's Day brunch, wearing a crop top and cut off denim shorts, on Sunday (08May16).

"Making brunch with my favorite mama," he captioned the sweet shot of the toned model.

The post caught Kelly's eye and the singer, who has previously struggled with her weight, took to Twitter to express her jealousy at Chrissy's ability to bounce back from pregnancy so quickly.

"Okay, what?! She just had a baby," wrote the stunned 34-year-old singer. "My train of thoughts.... #hateher #justkidding #kindofnotkidding". She also added the hashtag "#jealouslikeJonas", referencing pal Nick Jonas' hit song Jealous.

Kelly went on to invite John, Chrissy and little Luna over for a play date with her boy Remington and daughter River, who turns two in June (16).

Commenting on another of John's photos of a platter of fried chicken, she quipped, "Yeah I'm not gonna lie, that looks damn good! You & @chrissyteigen r welcome 4 play dates if u bring that w/ (with) you ha (sic)!"

Clarkson struggled through her second pregnancy and had to decide whether to perform on American Idol's final season or attend the Grammy Awards after her doctor advised the singer she couldn't do both in the weeks before labour.