Kelly Osbourne's friend and 'Fashion Police' co-star Joan Rivers has told Lady Gaga to "lighten up" after she publicly berated the lilac-haired star for "bullying" on the E! TV series.

Earlier this week, Gaga took a swipe at Osbourne in an open letter shared via her website LittleMonsters.com.

In the post on January 10, famously eccentric singer Gaga wrote to Osbourne: "Your show breeds negativity, and over the years has even become comedic in nature [...] What about your body revolution? It used to make me truly sad when I would hear people talk about your weight when you were younger, as I was bullied too. To see you blossoming into a beautiful slender woman who makes fun of others for a living is astounding. Why not help others?"

After Kelly's mother Sharon jumped to her daughter's defence yesterday, the reality TV star's 'Fashion Police' co-star Rivers told Entertainment Tonight: "’Fashion Police’ is a comedy show. Anyone that comes out of an egg should figure that out,“ before adding: "Lighten up.”

Osbourne matriarch Sharon also responded to Gaga's open letter yesterday, telling the international superstar: "I must say your opinions on what is politically correct and acceptable totally differ from mine, but that is what makes the world so interesting…we are all different. How sweet that you have empathy for my daughter, as you feel that she has taken a less passionate path in life. You say her work on E! with the Fashion Police is 'rooted in criticism, judgment, and rating people's beauty against one another.' Welcome to the real world.

She added: "Example, when I saw you wear a dress made out of raw meat, I was sickened. When I see you wearing fur, and using it as a fashion statement, the fact that defenceless animals have been killed so you can get your picture in the press is abhorrent to me."