So, I've been doing a massive rewatch of Classic Who. Started with Trougton, which I had seen very little of previously (Including the Reconstructions for the missing episodes), watched all the way through Pertwee, and just finished Key to Time last night. So, I was wondering, why exactly did they Regenerate Romana and switch over to Lalla Ward? I love both actresses in the role, and I love the explanation for the Regeneration in Gallifrey Adventures Audio Series, so I'm glad we got both of them. Just wondering, behind the scenes, why the change? Did Mary Tamm want to leave, or her contract ran out and re-upping her would've been too expensive or what exactly went on? Did they know when filming The Armageddon Factor that they were going to use the Astra Actress to continue the role of Romana, or was that a las minute afterthought when they had to replace Mary Tamm?