Kate Middleton's adorable nickname for Prince Louis will warm your heart

Prince William and Kate Middleton have an adorable nickname for their youngest son, Prince Louis. 

The sweet nickname was revealed during a family day out volunteering last year, where the whole Wales family dressed up in Scout outfits to mark the Big Help Out - a day of volunteering where the public is encouraged to get involved with local schemes. 

This was Prince Louis' first official engagement at the 3rd Upton Scouts Hut in Slough and the youngster looked in his element alongside his parents and siblings, trying his hand at archery and snacking on s'mores by the open fire. 

In footage of George, Charlotte and Louis gathered around the firepit for a s'mores toasting, the Princess of Wales can be heard using an adorable nickname for her youngest son.

"Pop that in the fire, Lou Bugs," she says in the clip. 

The sweet moment between mother and son was captured on camera and posted by a royal fan to social media site X (formerly Twitter) with the caption, "The sweetest video of Prince Louis tucking into a s'more. Love these natural family moments!"

Prince William was also present for the wholesome day out and in the background of the clip, viewers can hear him saying, "You've made his day," in reference to Louis tucking into his fireside sweet treat. 

Earlier at the event, Kate was heard using the sweet phrase again as Louis pushed around a wheelbarrow. "Well done! Good job, Lou bug!" the mother-of-three exclaimed. 

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Fans were quick to comment on the sweet video, with one saying, "Is that William saying you made his day? So cute." While another wrote, "It's the head flop as he tastes that sweet treat pure joy! Bet he's a great kid to be around, lots of fun and personality."

"A gorgeous little 5 year old boy who is acting exactly how he should at that age. He is so cute," a third added. 

Prince Louis isn't the only one with a special family moniker - Prince George also has the sweet, if not unusual, nickname, PG Tips.

Back in 2013, the Mirror reported, "Proud royal parents William and Kate have given their new son George an unusual nickname – after a brand of teabags. Pals started calling Prince George PG, so the couple took the next logical step and dubbed him Tips."

Charlotte also has a special nickname, with Prince William having previously been heard calling his daughter "mignonette", which means "delicate" in French.