Helen Worth, who plays Gail McIntyre in Coronation Street, said:
Geoff was a very dear friend for many years, and I'm very sad to hear the news of his passing. He was a master of gentle comedy and brought pleasure to so many people. He will be sadly missed.
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Mladic, now 75, was the military commander of Bosnian Serb forces in the 1990s, who fought against the Bosnian Croat and Bosniak armies.
Weather: Heavy rain and strong winds in the north
His representatives said Cassidy, who was hospitalised last week, died "surrounded by those he loved."