Kate Middleton Celebrating Her 36th Birthday ''Privately'' With Family

Happiest of birthday wishes, Kate Middleton!

The Duchess of Cambridge turns 36 today, and as a source reveals to E! News, members of the royal family have gathered at Kensington Palace to celebrate. Kate is "celebrating privately with [Prince] William and the children," the insider says, referencing 4-year-old Prince Georgeand 2-year-old Princess Charlotte. 

"It's just a quiet celebration at home," our source adds. "No big party."

Meanwhile, Prince Harry and Meghan Markle attended their first joint royal engagement of the new year today. The engaged pair arrived hand-in-hand to Reprezent 107.3 FM—a radio station that supports young adults through radio and broadcast training.   

The famous Brits have plenty of reason to celebrate this week. Aside from Kate's special day, Princess Charlotte began preschool on Monday. The palace released especially precious photos of the toddler as she prepared for her first day at Willcocks Nursery School in London, which were taken by her proud mom. 

"The Duke and Duchess of Cambridge are very pleased to share two photographs of Princess Charlotte at Kensington Palace this morning," a caption for the pictures read. "The images were taken by The Duchess shortly before Princess Charlotte left for her first day of nursery at the Willcocks Nursery School."

And in just a few short months, Princess Charlotte and Prince George will have another little sibling of their own! The Duchess announced her and Prince William's third child is due April 2018, just one month before Prince Harry and Markle are set to wed at St. George's Chapel in Windsor Castle. 

At the end of January, Kate and William will embark on their first Royal Tour of 2018 to Norway and Sweden. It's currently unclear whether the kids will come along for the four-day trip visiting Stockholm and Oslo. 

But for now, honor Kate's 36th birthday with a look back at her style evolution from her last decade in the spotlight.