Prince Louis Turns 3 — See Prince William & Kate Middleton's Youngest Son's Sweetest Photos

Prince Louis reached another milestone as he celebrated his third birthday. Here's a look at some of his most memorable moments shared with the public.

On April 23, 2018, the Duke and Duchess of Cambridge welcomed their third child, Prince Louis Arthur Charles, at St. Mary's Hospital. Their youngest son is fifth in line to the throne, following his older siblings Prince George and Princess Charlotte.

Shortly after his birth, Louis made his public debut while being carried by his mom, Kate Middleton, by the hospital's front steps. Prince William stood beside his wife and newborn as they had their photos taken by the press.

The royal couple released two more photos of Louis in the days that followed, including a picture with his older sister, gently kissing his forehead, taken on May 2, 2018, during the princess's third birthday.

The birthday celebrant flashed a big smile as he hopped on his red bike, ready to go.

In July of the same year, the royal couple followed generations of tradition by having their youngest child baptized in the Chapel Royal at St. James' Palace. Several photographs from the occasion were shared online, featuring Louis' "handmade replica of the Royal Christening Robe."

Photographer Matt Holyoak took the official pictures during the ceremony, including a family portrait complete with William, Middleton, and their three children. Another photograph with the other royal family members was taken but did not include the Queen and her husband, Prince Philip.

Before 2018 came to a close, the family-of-five gathered for a Christmas card picture taken outdoors. The royals wore blue and green color-coordinated outfits as they posed by the trees. Louis especially looked adorable standing on his mother's lap while giving a gentle smile.

The following year, the duke and duchess released new photos of Louis in time for his first birthday. The celebrant looked full of joy as he wandered outdoors while cozy in knitted long-sleeved tops.

More photos were shared on Instagram when the family visited the RHS Back to Nature Garden at the Chelsea Flower Show. Snaps of Louis getting up close with nature and holding a twig while running towards the camera.

"Over the past months, Prince George, Princess Charlotte, and Prince Louis have helped The Duchess gather moss, leaves, and twigs to help decorate @The_RHS Back to Nature Garden," the caption read.

Young as he is, Louis's love and understanding of nature have been rapidly growing as he often enjoys time outdoors. In 2020, the little prince met broadcaster and historian David Attenborough for the screening of his feature film, "David Attenborough: A Life On Our Planet."

The same year, Louis celebrated his second birthday in the most colorful way possible -- painting the rainbow on his hands. The toddler smiled as he showed his colored hands and face by the trees.

Before the year concluded, Louis again appeared alongside his older siblings, speaking on camera for the first time. The three kids conversed with Attenborough about animals in hopes that it would inspire others to take care of the planet.

It seems that time flew by so quickly as the youngest son of the duke and duchess of Cambridge is celebrating another milestone -- his third birthday. In a recent share, Louis looked adorable in an all-blue ensemble as he headed for his first day of nursery.

The birthday celebrant flashed a big smile as he hopped on his red bike, ready to go. Several fans could not believe how the young prince grew up before their eyes, as shared in the post's comments section.