Grammy-winning singer Celine Dion announced Tuesday she had canceled a string of upcoming shows in Las Vegas due to a virus-triggered problem with her vocal chords. The Canadian-born star was due to sing at Caesars Palace in a series of shows through March 18, but has called them off after being ordered to rest her voice for six to eight weeks. After difficulties last week forced her to cancel weekend performances, she decided to seek advice from laryngeal physiology expert Gerald Berke in Los Angeles. The five-time Grammy winner "flew to Los Angeles on Monday afternoon and had a thorough examination at Professor Berke's clinic," Dion said in a statement, adding that the doctor "diagnosed Celine with weakness in her right vocal chord, secondary to a viral illness." Berke prescribed resting her vocal chords "in order for Celine to completely recover from this condition," said the statement on her website. "I tried to sing at my sound-check last week, and I had no control of my voice whatsoever," said Dion, who is the mother of twin boys born in October 2010. "We thought that after a few days rest I would improve but it wasn't getting any better... I guess it was worse than I thought. I'm fortunate that I was able to see Professor Berke. "He identified what was causing the problems I was having, and he assured me that with the amount of rest he prescribed, I would be back to 100 percent." She added: "Obviously this is the worst thing for a singer... not being able to do your shows. I feel worse knowing that I'm disappointing my fans. I'm so sorry... I hope they forgive me." Dion expects to be back on form for her next run of Vegas shows from June 9 to August 19, said the statement, adding that fans with tickets for the cancelled shows will be offered refunds.