Prince Harry regrets losing a close bond with his sister-in-law Kate Middleton, especially after the Princess's cancer diagnosis.

As reported by Fabulous Magazine, royal expert Ingrid Seward claimed that the Duke of Sussex “thinks about the loss of his friendship" with the Princess of Wales.

She said, "I'm sure that Harry thinks about it a lot. It probably occupies a lot of his thinking time," as he "always wanted a sister."

Ingrid shared that the former working royal once said that Kate "was the sister" he never had.

The royal author shared that the late Princess Diana told her that Harry "always wanted a sister."

She said: "Harry always wanted a sister and I said, look, I can't just produce a sister for you Harry.'"

Ingrid believes Harry could reconcile his strained relationship with the ailing mother-of-three. However, the "ball is totally in Kate's court."

It is pertinent to mention here that Harry and his wife Meghan Markle sent warm wishes to Princess Kate after she announced her cancer diagnosis. 

The California-based couple's statement reads, "We wish health and healing for Kate and the family and hope they are able to do so privately and in peace."