Members of the royal family attended the service, including Prince Charles, Duchess of Cornwall and the Queen, at Westminster Abbey on Monday afternoon.
This was Meghan and Harry's final official engagement before they step down from their roles as senior royals on March 31.
They arrived at Westminster Abbey shortly before Prince William and Kate as they greeted the crowds.
Meghan looked stunning in a green Emilia Wickstead dress with her hair tied up in a sleek bun as she wore a matching green hat.
Why didn’t William and Kate greet Harry and Meghan back?
Shortly after their arrival, the Duke and Duchess of Cambridge arrived.
Kate looked glowing in a dark red Catherine Walker coat dress while William wore a navy suit.
As Kate and William headed inside the Abbey, they took their seats in front of Meghan and Harry.
In coverage on the BBC, Meghan is seen giving the couple a wave and a 'hello' alongside Harry.
But viewers claim William and Kate appeared to sit down without waving or saying hello back.
Sharing a video of the moment to Twitter, one person wrote: "Meghan is too gracious to smile to him they really pretend to not see them like the disrespect but I am happy because it shows what we know about the Cambridges."
Another said: "Wow Meghan said hi and I don’t think they returned the favour wow."
A third tweeted: "Why didn’t William and Kate greet Harry and Meghan back? Why are those two so rude?"
A fourth added: "Did Kate just ignore Meghan?"
Wow Meghan said hi and I don’t think they returned the favor wow !!
— Latoya (@Latoya2580) March 9, 2020
Why didn’t William and Kate greet Harry and Meghan back? Why are those two so rude?
— SarahGlas (@SarahGlas2) March 9, 2020
Did Kate just ignore Meghan?
— Marie (@iluvcha337) March 9, 2020
In the footage, it seems the couples did briefly acknowledge each other as they sat down.
Earlier this year, Harry and Meghan announced their decision to step back from royal life and divide their time between the UK and North America.
They also confirmed they will work to become "financially independent" and they will no longer use their royal titles.
They spent the new year in Canada with their 10-month-old son Archie.
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