The journalist, who has quit the BBC after 21 years, did not hold back as he took aim at the Royal Family. Mr Marr warned the monarchy faces a crisis when Prince Charles takes to the throne.
The broadcaster claimed some royals have not behaved well as they “assume the monarchy can never be questioned”.
However, he insisted the reason the institution is not questioned is because of the Queen.
Mr Marr told the Daily Mail: “When that terrible day comes that the Queen is no longer with us, the country will go into a state of shock.
“It will be like an ethical earthquake and I do not think it is fully understood or appreciated how this is going to be an absolutely massive moment in all our lives.
“It will shake the whole country in a way that will be hard to explain until we actually live through it.
“I know the Prince of Wales has plans for reforming the monarchy; it appears Charles and William will orchestrate a clear out.
“It won’t be the same: the modern monarchy under Charles has to earn its place every day, every week and every month in people’s affections.
“I’m sorry to say some members of the Royal Family have been behaving like free riders.
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Mr Marr announced he was leaving the corporation in November.
He is joining Global to present shows on LBC and Classic FM, and will also write for the left-leaning New Statesman magazine.
Mr Marr said on Twitter: “I think British politics and public life are going to go through an even more turbulent decade and, as I’ve said, I am keen to get my own voice back.
“I have been doing the Andrew Marr show every Sunday morning for 16 years now and that is probably more than enough time for anybody.”
Mr Marr joined the BBC in May 2000 as political editor and later spent 16 years at the helm of his own Sunday morning show.