Prince Philip warned Harry against tying the knot with Meghan Markle by telling him: "One steps out with actresses, one doesn't marry them," it is claimed.
The Duke of Edinburgh, 98, is believed to have made the outspoken remark to his grandson when it became clear the couple's whirlwind romance was serious.
But Harry, 34, ignored the advice and proposed, tying the knot with the former Suits actress, 37, in May last year.
It is also claimed that Prince William gave his own piece of relationship advice, asking his brother "Are you sure?" shortly before the Duke of Sussex proposed in 2017.
Harry and Philip are known to have a very strong relationship, and last week the Sussex's Instagram account wished "Grandpa" a happy birthday.
Philip was also featured in one of the couple's first pictures of baby Archie, alongside the Queen and Meghan's mother Doria Ragland, 62.
The Duke was one of the first people to see Archie as Meghan revealed during a brief interview during a photocall.
She said: "We just bumped into the Duke as we were walking by, which was so nice."
Philip also made a surprise appearance at their Royal Wedding, despite recovering from a hip operation at the time.
The revalation of Philip's comment comes as Prince Harry and Meghan yesterday posted an adorable photograph of Archie in a touching tribute for Father's Day.
In the sepia-toned image shared on the Sussex Royal Instagram account, six-week-old Archie can be seen cutely clutching the Duke of Sussex's finger.
The Prince's wedding band is also clearly visible.
Alongside the snap, which has so far been liked 1.8 million times, the caption reads: "Happy Father's Day! And wishing a very special first Father's Day to The Duke of Sussex © SussexRoyal."
It comes after it was revealed that Archie Harrison Mountbatten-Windsor is to be christened in Windsor next month in the chapel where his parents were married.
The previously unseen picture is the first glimpse the public has been given of the young royal since his toes appeared in an Instagram post on May 12, to celebrate Mother's Day in the US.
Meghan and Harry shared the image when Archie was less than a week old.
The post of the baby's feet in front of forget-me-not flowers was liked more than two million times on the social media site.
It was captioned: 'Paying tribute to all mothers today, past, present, mothers-to-be, and those lost but forever remembered. We honour and celebrate each and every one of you.'
Buckingham Palace did not comment on Philip's alleged quote.
Philip's alleged comments were reported in The Sunday Times in a magazine article about the so called "rift" between the Harry and Meghan and Kate and William.
The article by journalist Sophia Money-Coutts featured comments from royal insiders about the relationship between the Fab Four, amid rumours they are set to divide their Royal Foundation charity.
Ms Money-Coutts is a former writer at society magazine Tatler and daughter of retired private banker Crispin Money-Coutts, 9th Baron Latymer.