Sharon Osbourne failed to mentor a winning act
Sharon Osbourne has announced that she is stepping down as a judge on The X Factor after four series.
In a statement she thanked fellow judge Simon Cowell and "the wonderful British public for their enormous support".
The wife of rock star Ozzy was also joined on the panel by Louis Walsh and, in the last series, by Dannii Minogue.
"She has been a tremendous judge and mentor on the programme, but we respect her wish to leave and wish her the very best," an ITV spokesman said.
"ITV thanks her for her immense contribution to the show and for all her humour, compassion and energy."
Osbourne was rumoured to have clashed with her fellow judges, and during the most recent run, she walked out of a show when two of her three acts faced the axe.
Host Dermot O'Leary told viewers that she was unable to choose between her singers and left the remaining judges to make a decision.
A spokesman for the show said at the time: "She was very upset last night. All we can say at this stage is that we're hoping she'll be back for next week."
In 2005, Osbourne threw two glasses of water over Louis Walsh after he criticised one of the competing acts, Journey South, and made derogatory comments about her husband Ozzy.
Osbourne has not produced a winning act in four series of the programme.
The 2007 season was won by Scottish singer Leon Jackson, mentored by Dannii Minogue.