Kelly Osbourne has defended Miley Cyrus after she was filmed smoking a legal high.

The TV star insists her friend and `So Undercover' star has learned her lesson after video footage showing the 18-year-old singer-and-actress inhaling smoke from a bong - a filtration device for smoking - was posted on the internet.

Kelly tweeted: "This really makes me mad. Miley is one of the most hard working respectful women I have ever worked with I am learning a lot from her!

"Miley and I have become really close I'm sick of all the haters judging her she made one mistake and trust me she has learned her lesson!"

Kelly revealed she decided to speak out after hearing rumours her mother, Sharon Osbourne was worried about Miley's influence on the 26-year-old star, insisting her new pal encourages her to lead a healthy lifestyle.

She added: "Just read in the rags that apparently my mum thinks Miley is a bad influence on me it could not be father from the truth!

"Actually it's the other way around Miley has us all on a health kick. Gym/early nights There really scraping the barrel on that one! (sic)"

Reality TV star Kelly then admitted she was a bad influence on the former `Hannah Montana' actress, posting a picture on her twitter page showing the pair giggling over cupcakes.

She captioned the image: "This is how I'm a bad influence on Miley...I force her to eat cupcakes so I don't feel so bad about eating one!"