Prince William's birthday celebrated with release of previously unseen photo from coronation rehearsals

The British royal family marked Prince William's 41st birthday on Wednesday by releasing a previously unseen photo with King Charles.

The sweet father and son moment was captured inside Westminster Abbey during last month's coronation rehearsals.

In the relaxed and unguarded moment, the Prince of Wales and the King are seen sharing a laugh as William appears to struggle with fastening an ancient Imperial Mantle over his dad's shoulders.

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The pair are seen in their suits just days before the big ceremony, which saw them both donning ceremonial robes for the historic occasion.

"Wishing The Prince of Wales a very happy birthday today!" the tweet read.

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William's birthday marks his first as heir apparent and Prince of Wales after the title was bestowed on him last September following Queen Elizabeth's death.

Just like the official portraits released after the coronation, this image still makes a point of the line of succession and future of the monarchy by only including the monarch and his heir.

The photo comes days after William and Kate released their own new family photos for the UK's Father's Day.

It showed the father-of-three surrounded by and cuddling Prince George, nine, Princess Charlotte, eight, and Prince Louis, five.

While it's not known if younger brother Prince Harry will reach out to the birthday boy amid their on-going fallout, it's been reported that the Duke of Sussex is highly likely to at least send a text to his big brother.