Aaron Carter has shocked fans with his incredible image and body transformation on Instagram, which he says has left him feeling ''amazing.''

The 29-year-old US singer – who shot to fame as a child star in the early 1990s and later a teen heartthrob with a chiselled six pack – showed off a fuller physique on the social media platform.

Carter has had a particularly tough year, recently completing a stint in rehab for ''legal and personal matters''. But things appear to be looking positive for the singer with new music is on the way.

In a before and after split picture, Carter is seen looking defined and toned, albeit underweight, in the left snap, while the updated shot shows him looking slim and healthy with a new green hairdo.

He captioned it: ''This is my before and after pics.
I went from 115 to 160 pounds in two months I feel amazing. 2018 I'm ready for you!! My new Music is on its way! ''

Carter's transformation, along with the ditching of his trademark flaxen locks and announcement of new music, was a lot for his 336K followers to take in.

One commented: ''looking good aaron!! gettin better!! you're inspiring!''

Another said: ''You look so healthy and at ease we are so proud of you keep up the good work ''.

A third added: ''@aaroncarter you look absolutely AMAZING!! Keep it up, stay strong and have faith. Most important, be happy with yourself ''.

The I Want Candy hitmaker has been laying low on social media for the past few months, and hadn't posted a picture on Instagram since 16 August.

Carter has hit the headlines for his personal life rather than music in recent years, being arrested in 2008 for speeding, when authorities found less than two ounces of marijuana in his car.

In July earlier this year, he was arrested in Georgia on suspicion of driving under the influence and marijuana charges, according to law enforcement.

Later that month he discussed his health issues, namely a hiatal hernia and lactose intolerance, along with confessing to using facial fillers. He also came out as bisexual on Twitter in August.

Aaron Carter
Aaron Carter has tested negative for HIV. Getty