The Are Lingus jet suddenly appeared into view while the crowds were filmed from above by the National Police Air Service.
And the dramatic sight of the huge plane thundering past below them came as something of a shock to the NPAS crew on the helicopter.
They tweeted: ‘That awkward moment where you’re innocently scanning crowd numbers around the Royal wedding and a plane several thousand feet BELOW us scares me for a split second!’
Tweeters also reacted with shock at the plane photobombing the Royal Wedding crowds:
The plane was flying between 1,000 and 3,000 feet as it made its descent towards Heathrow Airport, while the police chopper was flying at over 8,000 feet.
The NPAS kept a close eye on the thousands who turned up to catch a glimpse of Prince Harry and Meghan Markle as they took to the streets in a procession following the glitzy ceremony.
Some 100,000 lined the streets of the Berkshire town as the newly-married couple made their way to their wedding reception.
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The NPAS provides air support to the 43 territorial police forces across England and Wales.
The newly married Duke and Duchess of Sussex will have little time to recover from their fairytale wedding as they head straight back to work this week.
Unlike other newlyweds, Harry and Meghan will not be jetting off on a honeymoon straight away, and will instead be back on royal duty, carrying out their first official engagements as husband and wife.
The couple, who exchanged vows in a ceremony watched by millions across the world on Saturday, are due to attend a Buckingham Palace garden party on Tuesday as part of the Prince of Wales’s 70th birthday celebrations.
It will mark the beginning of a new life for former actress Meghan, who has already spoken of her desire to ‘hit the ground running’ in her role as a full-time royal.
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