Few will have heard of Patrick Rock before now - except for those in the Tory Party's high command.
At 62, he has had a political career spanning four decades, working with senior party figures such as the former Tory leader Lord Howard, and the former party chairman, Lord Patten.
When the Prime Minister told me today he was "profoundly shocked" to hear of the allegations against Mr Rock involving images of child pornography, that was probably an understatement.
Mr Rock has been a confidant and adviser to David Cameron since the 1990s. The Prime Minister brought him back into the heart of government in 2011 as number two in the policy unit, where Mr Rock worked on issues which included internet filters to protect against child abuse images online.
David Cameron said he had to be careful what he said today because this was an ongoing criminal investigation.
But there was no disguising the fact that - whatever the outcome of the investigation - Mr Rock's arrest and resignation are a serious blow, both personally and professionally.
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