The Duchess of Sussex mouthed "hello" to Kate as she found her seat at Westminster Abbey for the Commonwealth Day Service.
Harry also said "hello" and smiled at his brother before sitting next to his wife.
Sophie Wessex, who was seated behind Kate, leaned in to chat with her, while Harry and Meghan caught up with Prince Edward.
MEGHAN MARKLE, PRINCE HARRY MAKE LAST ROYAL APPEARANCE, BARELY INTERACT WITH PRINCE WILLIAM, KATE MIDDLETON
Meghan later chatted animatedly to Edward as they waited for Queen Elizabeth II to arrive, with Harry joining in the conversation and putting his arm on the back of Meghan's chair as he did so.
This time last year Meghan and Kate greeted each other with a kiss on each cheek, but this afternoon was a slightly more reserved display.
They were also shown their seats rather than walking behind the queen like last year.
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A source said the sudden change was made Monday, despite the Order of Service already having been signed off and printed.
The celebration will be the last royal engagement for the Sussexes before they start their new life in Canada.
There have been rumors of a rift between the two royal couples, with tensions allegedly rising with the announcement of Harry's departure from the royal family.
William and Kate were reportedly "incandescent with rage" when they found out the Sussexes plans to leave after the news had been shared with the public.
Prince Andrew, who attended the service last year, was also missing after stepping back from royal duties amid criticism over his friendship with convicted sex offender Jeffrey Epstein.
Kate later changed into an elegant sapphire blue embellished gown as she hosted a reception at Buckingham Palace this evening.
The Duchess of Cambridge rewore her stunning Indian-inspired bespoke Jenny Packham gown to celebrate the 25th anniversary of the children's charity Place2Be.
The last time she wore the gown was at the Bollywood Gala in Mumbai during her tour to India and Bhutan in 2016.
The Sun revealed that the queen and Prince Harry had a four-hour long heart-to-heart talk at Windsor Castle on Sunday about his future.
She told him over lunch that he would be welcomed back if he and Meghan ever decided to rejoin the royals.
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It has also been reported that Prince Harry's relationship with his dad is "rock solid" despite quitting royal duties.
The Duke of Sussex has spent hours with Prince Charles since returning to the U.K. last week to fulfill his final duties as a royal before quitting the Firm.
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Meghan gave a surprise appearance at Robert Clack School, Dagenham, East London, on International Women's Day on Sunday.
It was her final solo engagement as a royal — Meghan urged her young audience to “speak up for what is right.”