Image copyright Reuters

The Queen was clad in full ceremonial robes as she delivered her speech at Parliament's State Opening.

But one thing was missing from her elaborate outfit: the jewel-encrusted Imperial State Crown.

Instead, she wore the diamond diadem recognisable from her profile on British stamps and coins, while the crown rested on a table beside her.

The decision didn't go unnoticed on social media.

Skip Twitter post by @kateferguson4 The Queen wore the State Diadem (pictured right) for today's Queen's Speech. It is only the third time she has not worn the Imperial State Crown (pictured left) since 1952 pic.twitter.com/ikKG4FVx5M — Kate Ferguson (@kateferguson4) October 14, 2019 Report

The choice was a matter of personal preference for the 93-year-old monarch.

The diadem is much lighter than the crown.

The tiara is traditionally worn for the journey to and from Parliament.

The crown, which was commissioned for the Queen's father, George VI's, coronation in 1937, boasts nearly 3,000 diamonds, 17 sapphires, 11 emeralds and around 270 pearls - in addition to the large diamond, ruby and sapphire that adorn the back and front.

It weighs about a kilo.

The rim of the George IV State Diadem, however, is about a quarter of the width and set with around 1,300 diamonds and 170 pearls.

Media playback is unsupported on your device Media caption A look at the fanfare and formality behind this year's State Opening of Parliament

The Queen commented on the weight of the crown, which she wore at the end of her coronation and for most State Openings of Parliament since, in a BBC documentary last year.

She described it as "unwieldy".

"You can't look down to read the speech, you have to take the speech up, because if you did your neck would break - it would fall off," she said, smiling.

"So there are some disadvantages to crowns, but otherwise they're quite important things."

Media playback is unsupported on your device Media caption "You can't look down" while wearing a Royal crown, the Queen tells royal commentator Alastair Bruce

Royal commentator Richard Fitzwilliams said the decision not to wear the crown was a "practical alteration" to the Queen's schedule that was "part and parcel of the monarch growing older".

"There's no question that it's just a matter of accommodating advancing age in as dignified a way as possible," he said.

Victoria Murphy, journalist and author, said there have been a number of "gradual tweaks" to the Queen's schedule as she grows older.

For example, she first took the lift instead of the stairs at the State Opening of Parliament in 2016, and Prince Charles has laid the wreath at the Cenotaph on Remembrance Day since 2017.

However, the Queen made clear in a speech when she was 21 that she "sees her role as a duty for her whole life", she added.

Image copyright VT Freeze Frame Image caption The Queen delivering her speech at the State Opening of Parliament in 1988, alongside Prince Philip

The Queen's Speech is the key part of Parliament's State Opening - when the monarch reads a speech written by ministers setting out the laws the government hopes will be approved by Parliament during the coming session.

Since 1852, it has been tradition for the monarch to arrive at Parliament in a gold carriage escorted by the household cavalry - about 120 horses - and in full traditional dress.

The crown and ceremonial accessories were absent from the Queen's outfit in 1974, following then-prime minister Ted Heath's decision to call a snap election.

The whole event was also scaled back in 2017, three weeks after former prime minister Theresa May also called a snap election.

Then, the Queen arrived in a car rather than her carriage - there was too little time to rehearse the horses because Trooping the Colour had taken place four days earlier.

She wore a blue jacket and hat, much remarked-upon in the wake of the Brexit vote, rather than the crown.

Image copyright Reuters Image caption The Queen delivering her speech at the State Opening of Parliament in 2017 alongside Prince Charles

This year the crown was delivered to Parliament in its own carriage and remained at the Queen's side as she delivered the speech.