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The performer was apparently filming the Judges' Houses stage of the show in Dublin when he decided to go back to Australia, escorted by a producer.
A source told News.com.au: "On arrival in Dublin it was decided that Matthew needed to return to Australia to the care of his family."
A Seven spokesperson added: "Matthew had a strong commitment to the programme and has tried his utmost to make it work. He has the support of his family and friends as he works his way back to full health."
The auditions and Boot Camp stages of the show have already been filmed with Newton as the host, ahead of the show's August 30 premier on Seven.
