Royal Editor Chris Ship reports on a historic moment for Charles
It was a moment of change.
The last time an heir to the throne read the speech on behalf of the Monarch at the State Opening of Parliament, it was 1819.
The future Queen Victoria had just been born and the Prince Regent, who had been acting for his father for nearly a decade, was still a year away from being crowned King George IV.
203 years later, it happened again.
ITV News Royal Editor Chris Ship rounds up the significance of the moment
And so, walking behind the Imperial State Crown on Tuesday was not the Sovereign, but her two appointed Counsellors of State: the Prince of Wales and Duke of Cambridge.
The choreography was changed this morning when the Queen's throne was taken out of the Lord's chamber.
That left the Consort's throne for the Prince of Wales - and when he sat down he town a long look at the Imperial State Crown which had been placed to his right.
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After so many years as heir to the throne, Charles would have known what a symbolic this moment this was.
Similarly, Black Rod - the senior officer from the House of Lords - had to change her summons to MPs when she strode into the House of Commons.
"Mr Speaker", she said: "The Queen commands this honourable House to attend her Counsellors of State immediately in the House of Peers."
When MPs arrived in the Lords, the speech he went on to read, which is always written by the government, had undergone a last minute rewrite.
It changed all the references of "my government" and "my ministers" to "Her Majesty's government" and "Her Majesty's ministers".
Prince Charles appeared solemn, as well he might, given this was the first time he had acted for the Head of State at this occasion.
But then he has grown accustomed to standing in for the Monarch.
Watch Prince Charles deliver the Queen's Speech
Prince Charles has replaced the Queen at the Cenotaph on Remembrance Sunday, he's stood in for her at the Royal Maundy Service, he's been the most senior royal at a number of events such as the Commonwealth Day service and the church service on Christmas Day and he's been the most senior travelling member of the family for many years.
The Queen gave up international travel in 2015. So today felt like we were watching the next chapter of the long and gradual transition from one Sovereign to the next.
The Queen, we are told was watching from Windsor. She will have felt a mix of emotions: disappointment that she could not attend given she has not missed this ceremony since 1963.
And also pride that two future Monarchs, her son and grandson, did the job for her and kept alive a tradition which can be traced back to the 16th century.