Lady Gaga has revealed why her recent letter to Kelly Osbourne was made open to the public.

As previously reported, Gaga penned an open message to the Fashion Police star after believing that Osbourne got in touch with her about being bullied by the 'Born This Way' star's fans on Twitter, slating her TV show and criticising her apparent negativity.

Mother Sharon Osbourne then wrote to Gaga to confirm that it was her that contacted her manager over online bullying, before taking shots at the singer.

The 'ARTPOP' star took to Twitter last night (January 12) to state why she made her original letter to Kelly Osbourne public. She said:

"The "real world" can be cruel, why not try to change it into a better place? I am an activist. Nobody takes adolescents seriously, I do."

The singer continued: "My letter to @MissKellyO was open, because her statements on cyber-bulling were public & as a youth activist I'm compelled to be involved."

Gaga later tweeted that she has been working in the studio a lot recently, adding: "Was up all night with the boys in the studio. Inspired. @madeon just joined the gypsy life too. This is gonna be the best leg yet!"