Subtle way Princess Kate sends strong signal to Prince William that 'speaks volumes'

Princess Kate's choice of picture for her husband Prince William's birthday is a testament to their strong bond, according to a royal expert.

"Happy birthday Papa, we all love you so much!" Kate wrote in a heartfelt tribute, accompanied by a playful photo of William and their children jumping across a sand dune. This snapshot, celebrating William's 42nd birthday, conveys more than just a moment of family fun.

Royal expert Jennie Bond reflected on the significance of this particular birthday photo.

"The last few months have been a test of their strong partnership," she said. "I think this photograph tells us that they are still able to jump for joy, even in the toughest of times, and that Kate has deliberately chosen a picture that speaks of their optimism for the future.

"She adores William - he is her rock and has supported her so selflessly through all of this and has taken flak from members of the public for not doing more and for devoting himself to her. So she adores her man. I think their marriage is stronger than ever."

Reflecting on Prince William's difficult upbringing, Jennie told OK!: "It's fabulous for William to be in such a happy marriage, having grown up in a house that was, broken in so many ways and to have witnessed the breakdown at very close quarters of his parents' marriage.

"He had to comfort his mother during difficult periods and that is something that no father would ever want to put his own children through."

Fortunately, William was able to marry for love.

"As we know, William relishes his own model of family life. These past few months have been probably the most testing time in the whole of their marriage and must have shaken them to the core", Bond said.

"To think about the future must have been incredibly unsettling, but I think that picture has been deliberately chosen to show that they are now all in a frame of mind whereby they can look to the future with positivity."

Since Princess Kate's cancer diagnosis being announced, Prince William was granted the option to step back from royal duties and focus on his wife and three children.

"It's a great accolade to a person to have your partner who has such a public role but any partner just say 'OK, I don't care what people say, you are my priority'", Bond said. "William has made it absolutely clear that Kate and the children are his number one priority and nothing is going to move him away from that path.

"It was a delicate situation for him and he did get some criticism, but that's quietened down now. So it was brave. And I think that's what Kate sees in her man - someone who is courageous and a very, very loving husband, as well as her best friend."