Kelly Clarkson has thanked Carrie Underwood for making her ''feel really thin'' after she was sent some clothes which didn't fit her.

The 36-year-old singer took to Twitter to send her heartfelt thanks to the fellow musician after she received a package from Carrie's activewear and accessories line, CALIA.

She captioned a clip of herself opening the package: ''Thank you @carrieunderwood. This apparel cake idea was adorable! I'm just now receiving it because it's been at Starstruck! Love all your gear girl! #Calia #FannyPackForTheWin''

The gifts were sent to the 'Because of You' singer in celebration of the brand's third anniversary, and gushed over the adorable box design, which was shaped like a five-tier cake.

Kelly also revealed how the clothes inside the package were now too big for her as she's begun to lose weight, and credited Carrie with giving her a confidence boost thanks to the loose clothes.

She said: ''Carrie Underwood, this is adorable. I don't know if you came up with this, but your company is turning three, congratulations!

''I love all your stuff you always send me. It's a cake. It's in the shape of a cake because they're turning three, y'all. Who came up with this? That's adorable. Each one is a drawer with a gift.

''And Carrie Underwood, thank you as well because I've lost weight since you sent this. So it's all too big for me which made me feel really thin. But I'm gonna find someone that loves it.''

Kelly's weight loss comments come after she recently vowed never to be afraid to show people what she ''really looks like'' because ''everybody'' has their flaws.

She said: ''[Full hair and make-up] is actual fake news. I think that sometimes Hollywood can be very 'Oh, we don't want people to see what we really look like. That'll be the death of you or something.' And it's like, 'Whatever!' Everybody poops. Everybody burps. Everybody's the same.''