The popular star made the move after re-thinking comments that she made on the ITV programme earlier in the week.
Alison shared her regret at making light of disruptive theatre audiences, explaining she hadn't realised the gravity of the situation.
Posting white text against a simple dark background, the presenter wrote: "After reflection on the comments I made on Wednesday's show I want to apologise to anyone who I offended, especially the incredibly talented theatre performers, who I have the utmost respect for.
"I had no idea the level of disruption audiences were causing and tried to make light of the topic on Wednesday's show, for that I'm truly sorry. I'm a great supporter of theatre and the arts and would never sing at the top of my lungs in any performance.
"I was wrong in what I said and I've given this a lot of thought over the past few days and believe I was wrong.
She went on: "On Thursday evening I attended a performance of the GBBO the musical which I absolutely loved and gave it a standing ovation, theatre is a magical experience for me and my family.
"I want to use my platform for good as always and want to stand up with the performers, front of house and theatre staff especially after seeing what happened at The Bodyguard in Manchester which has made me sick to my stomach.
"Once again I'm truly sorry but trust me I will do better in the future. Alison x."
Police were called to a performance of The Bodyguard on Friday evening where some audience members were removed and the performance had to be halted early, with one Twitter user describing the scene as a "mini riot".
Alison had previously discussed rowdy theatre audiences with co-star Vanessa Feltz, saying: "Staff are taking this very, very seriously and inflicting these rules. They are regularly walking up and down the aisles before the performance and during the interval with 'no singing' signs' I mean, I can't believe it, I'd be devastated."
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