Avicii's secret girlfriend has penned a heartbreaking 17-page letter following his tragic death.

The Swedish-born DJ - whose real name is Tim Bergling - was just 28 years old when he was found dead in Muscat, Oman, on April 20, and whilst a cause of death has not yet been confirmed, a statement from his family which includes the words ''he could not go on any longer'', seemed to hint at suicide.

Although it was believed Avicii was single when he died, Czech model Tereza Kačerová has confirmed they were in a relationship and has written a touching essay on her social networking sites to pay tribute to her late beau.

Alongside a slideshow of pictures of the DJ - which included one of him and her son Luka - she wrote: ''Dear Tim, I've spent the last days waiting to wake up, waiting for someone to tell me that this is some sick joke, some awful mistake. I think it's finally settling on me now that I will truly never get to see you again.

''The first couple of days I harassed your friends (are they SURE IT'S REAL?!, demanding proof, WHERE ARE YOU NOW?!) and googled articles to read that they had it all wrong. Every time I saw ''RIP'' and ''Avicii'' together in one sentence or an end date to your life, I felt shock all over again.

''When I saw they had changed your bio on Wikipedia from ''is'' to ''was'', I sobbed. I'd stare at it for minutes at a time, trying to decipher why it says that you died on April 20, 2018. It didn't make any sense. You are too young and wonderful and I love you too much for you to have that written by your name. (sic)''

The blonde beauty went on to explain why she and Avicii had decided to keep their relationship hidden from the public because it was theirs, but they were very serious as they were planning to have children together.

She explained: ''I was always very set on keeping our relationship private because I wanted it to be OUR and ours only and wanted no part in that madness. But I thought, if I'm going to share this with the world, it will be when I'm pregnant with our child. Ohhh how that plan went awry. (sic)''

Tereza also commented on Avicii's strong bond with her son Luka and how she hopes he will one day return to earth to play with the youngster again because she'll never let him forget the 'Wake Me Up' hitmaker.

She said: ''I used to tell you that Luka will never remember a life without you. Now I hope that he will remember his life with you. I'll be there to remind him. I'll show him. I read that before he died, Thomas Edison came out of a coma, looked upwards and said ''it is very beautiful up there''. I take comfort in that. Rest in peace Tin. Try to come back to Earth soon so that you and Luka can play together again. (sic)''