Diana, who died in a Paris car crash in 1997, is buried at her childhood home Althorp in Northamptonshire.
A spokesperson for the Duke of Sussex confirmed he arranged for flowers to be laid at her grave for Mother’s Day.
Harry’s brother Prince William also paid tribute to their late mother today.
The Duke and Duchess of Cambridge shared touching cards on social media from their three children Prince George, Princess Charlotte and Prince Louis to their “Granny Diana”.
The post on William and Kate’s Kensington Palace Twitter and Instagram accounts said: “This year Mother’s Day will be different once again.
“Many of us will be apart from our loved ones, but looking forward to a time in the not too distant future when we can give our mother a hug again.
“But for those experiencing bereavement, today may be particularly challenging.
“Each year on Mother’s Day, George, Charlotte and Louis make cards remembering their Granny, Diana, for William.
“Whatever your circumstances, we are thinking of you this Mother’s Day.”
George’s card features a drawing of a landscape with a tree, the sun, and birds flying in a blue sky.
It says in neat handwriting: “Dear Granny Diana, Happy Happy mothers day. I love you very much and think of you always, Sending lots of love from George xxxxx.”
Charlotte’s card, which is decorated with butterfly and flower stickers, says: “Dear Granny Diana I am thinking of you on mother’s Day. I love you very much. Papa is missing you. Lots of love Charlotte xxxxxxxxx.”
Louis’s card features a painted drawing of a heart and is adorned with animal stickers. It says: “From Louis.”
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