The world watched on television as flames tore through Windsor Castle's fortress, parts of which are almost 1,000 years old.
Priceless artwork was at risk and so were stately rooms, some of those were destroyed and a large restoration project followed.
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In a wide-ranging Peston on Sunday interview, he said Parliament security needs reviewing and the PM's counter-terror strategy is flawed.
The terror attack carried out by Khalid Masood at Westminster that left four people dead lasted less than two minutes say police.
Two knives were found at the scene in Islington, North London, and the suspects fled on foot before being arrested.