Never before seen photos of Princess Diana aboard Valentino yacht revealed

Italian businessman Giancarlo Giammetti shared the snaps on his Instagram page. Photo / Supplied

Never-before-seen photos of Princess Diana relaxing on board a yacht have been shared on Instagram.

The snaps, shared by Italian businessman and Valentino co-founder Giancarlo Giammetti, show Diana wearing a bikini and smiling alongside him and Prince Kyril of Preslav, reports Metro UK.

The photos were taken in 1990 in Italy, just two years before Princess Diana separated from Charles, according to The Sun. Giancarlo shared the photos to his personal Instagram page.

The snaps are thought to have been taken aboard the private Valentino yacht T.M.Blue One. The island of Stromboli off the north coast of Sicily can be seen in the distance.

Alongside the pictures Giancarlo wrote, "And here two moments of friendship with her, Princess Diana."

He shared the snaps out of nostalgia, as the relationship between Princess Diana and Prince Charles has recently been brought to light again in Season 4 of The Crown.

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One royal expert has disputed the Netflix show's claims he cheated on Diana during the marriage, claiming Charles was "really faithful" to her.

The marriage, which lasted 15 years, was full of ups and downs amid claims Charles had cheated on Diana with Camilla Parker-Bowles, now the Duchess of Cornwall.

Asked if he had remained "faithful and honourable" in his marriage, Charles said, "Yes, absolutely. Until it became irretrievably broken down, us both having tried."

But The Crown portrays the prince, played by Josh O'Connor, in the midst of an ongoing affair with Camilla (Emerald Fennell) in the early years of his marriage to Diana, played by Emma Corrin.