From Tim to Kim:
The pop singer - born Tim - is well known in Germany for having started hormone replacement therapy as part of her gender transition by the age of 12.
Now 16, she completed Gender Reassignment Surgery in November, according to a posting on her blog.
Girl in a boy's body: Pop singer Kim Petras, 16, may have become the world's youngest transsexual after completing gender reassignment surgery last November
Dr Bernd Meyenburg who heads the Psychiatric Special Outpatient Clinic for Children and Adolescents with Identity Disorders at the University of Frankfurt Hospital said: 'Very few youth psychiatrists have any experience with transsexual developments. The families wander from one psychiatrist to the next.
'I was always against such operations on children so young but after seeing how happy one of my patients was and how well adjusted after returning from having the operation abroad while still a teenager – I realised that in some cases it is the right decision.
'Kim is such a case – she always knew what she wanted.'
Kim herself said: 'Everything has changed because of this operation. I just can't wait to put on my favourite bathing suit and go swimming like I've never done before.
'I had to wait until my 16th birthday but once that was past I was able legally to have the operation.
Kim Petras pictured as a young boy
'I know that because of my past people will always bring up the subject, I can't get away from it. But I hope that one day I might be better known for something else like my music.'
In Germany, such operations are not usually allowed until the patient is 18.
However Kim managed to convince doctors when she was just 12 that she should have the surgery.
By 14 she was officially registered as a girl - and was already famous for her choice.
The costs of her procedure were covered by health insurance as her condition was officially diagnosed as an illness.
Dr Achim Wuesthof, an endocrinologist specialising in children and adolescents, who was treating Kim at a clinic in Hamburg, said that he and his colleagues felt that in this case it had been best to start earlier.
He said: 'To the best of my knowledge, Kim is the youngest sex change patient in the world.
'According to German law, two independent psychiatrists must confirm that the child is indeed transsexual and approve the sex change. Once that has been done, it is best to start as early as possible.
'Transsexuals experience the onset of puberty, and the physical changes it brings, as a serious trauma.
'But there is a general lack of empathy with cases like Kim's, mostly because people know little about the condition. Imagine a man that suddenly starts growing breasts or a woman that starts growing a beard against their will – that is how Kim and people like her experience puberty.
'They are not freaks, nor do they suffer mental illness. They are simply trapped in the wrong bodies. That is why it is best to help them as early as possible and reduce the trauma for them and their families.'
Last year Kim was signed to Joyce Records and released online her first single 'Last Forever'.
It became a YouTube and MySpace hit.
In September - just weeks before the cosmetic surgery finalising her transition from a male to a female -she released her first commercially available single 'Fade Away' into the German market.
Kim said: 'I was asked if I feel like a woman now – but the truth is I have always felt like a woman – I just ended up in the wrong body.
'I had a problem because I couldn't wear skinny stuff, but now I can wear whatever I want to. I really am looking forward to going swimming like everyone else and to wearing tight jeans that show off my figure. They are so tight, I always felt quite uncomfortable in them until now.
'Now I can go as tight as I want to. I used to wear mini skirts too, but yes, now even the tight ones can be part of my wardrobe.
'I can enjoy swimming, and bikinis, go in the changing rooms without a problem, everything has changed because of this operation. I just can't wait to put on my favourite bathing suit and go swimming like I've never done before.'
Kim, who is now studying fashion design, began calling herself a girl when she was just two years old.
Her father Lutz said: 'I suppose it took me longer than my wife to accept it, but Kim is a very persuasive girl, she knows what she wants and how to get it.
'I am very proud of what she has achieved, how she has managed to get there and how she sticks to her dreams no matter how hard and painful they are to follow.'