Prince William seen kissing Kate Middleton's hand

Prince William and Kate Middleton attended the Royal Variety Performance in London on Wednesday.

The couple stepped out in matching velvet looks for the rare joint appearance.

Though the couple avoid public display of affection due to royal protocol, William and Kate were caught sharing a secret intimate moment before stepping out of their car.

A video widely circulated on social media shows William quickly kissing his wife on the hand.

Speaking to The Express, body language expert Judi James said, "Kate and William are often at their flirtiest best when they are both fully glammed up for a red-carpet appearance and while Kate looks radiant here, William's body language appears slightly bashful as he walks beside her. "

She added, "His hands hang slightly in front of his torso and his puckered smile suggests he's slightly overwhelmed by the grinning glances Kate throws at him."

Judi James said, "Kate looks confident here, walking ahead to greet the hosts but with one eyebrow raised in that flirty signal as she looks across to William and he responds with a hand on her back in a gesture of steering and protection."