The Duke and Duchess of Cambridge exhibited rare sweet gestures in public, and the watchers went crazily happy about it.

Prince William and Kate Middleton participated in the Shout's Crisis Volunteer event at the Troubadour White City Theatre in London. Together with Prince Harry and Meghan Markle, the royal volunteers launched the 24/7 text message support project in May 2019 to support anyone in need.

During the event, Prince William and Kate learned that since the debut of the helpline, 75 percent of its callers were under the age of 25 -- with suicide topping the most frequent subject that was raised in the conversations.

"Catherine and I heard outside about how many of you are waking up at 3 am to answer the peak demand. The fact we've had to launch Shout shows just how in need the mental health sector is at the minute," Prince William said to formally close the event. He also acknowledged the efforts of his wife, Prince Harry and Meghan and congratulated the accomplishments of Shout.

After the off-the-cuff speech, attendees saw Prince William once extended his hand and touched Kate's arm. The duke also softly tapped the back of his wife and guided her to the car before leaving the venue.

Recently, a body language expert Patti Wood compared Prince Harry and Meghan Markle's intimate gestures to Prince William and Middleton's sweet and lovely signals -- which is an unspoken rule in royalty

Prince William, Kate Not Allowed to Display Affection?

Unlike Prince Harry and Markle who are always showing off their love, royals are expected to meet the "unspoken expectation."

In general, public display of affection is considered ill-mannered by the royals. The protocol is being practiced by Prince William and Kate most especially when they are in public.

The former butler to Princes William and Harry, Grant Harrold, told TIME once that it "depends on where the royals are and what situation they're in" if they want to hold hands or touch each other.

Harrold also said that Prince William and Middleton's casual touching during their Royal visit in Oslo, Norway was more natural and carefree than a formal and social event, such as Trooping the Color.

The British Royal family created etiquette rules which started since the establishment of the monarchy. As time went by, the members have adapted the decorum to show respect and courtesy while offering the best for everyone. 

For now, royal watchers are just happy to see that the soon-to-be-king finally display a little bit of love to his wife.

READ MORE: Royal Signals: Are these Prince Harry, Meghan Markle's Secret Signals?