The outlet also claimed Kate was "showered with gifts" by husband William, including a pair of diamond earrings.
It's a strong contrast to Kate's birthday last year, which was "ruined" by Harry and Meghan's announcement they were stepping down from their senior royal roles.
Royal writer Phil Dampier said her special day was undoubtedly wrecked by the Megxit news, telling The Sun: "Apart from anything else, Harry and Meghan's announcement has overshadowed Kate's 38th birthday."
The Duchess of Cambridge celebrated her 39th birthday on January 9 in style - with a nice hot cuppa.
Instead of marking the occasion with a weekend house party with friends at her country home of Anmer Hall like every other year, Kate is said to have spent a "quiet birthday" having a tea party organised by William and their three children, George, Charlotte and Louis.
The Queen, Charles and Camilla all offered birthday wishes to Kate on their social media.
The official Royal Family account posted two photos of Kate, writing: "Wishing the Duchess of Cambridge a very happy birthday today!"
Charles and Camilla shared another snap of the mum-of-three, writing: "Happy Birthday to the Duchess of Cambridge!"
Kate normally celebrates on the weekend closest to her birthday by throwing a shooting party and hosting her closest friends and family, including her parents, Carole and Michael.
Last year, William and Kate welcomed guests to a weekend-long celebration including a Sunday morning church outing with the Queen at St Mary Magdalene Church.
The Cambridges thanked friends and family for their birthday wishes in a following post on Instagram, acknowledging that it's a rough time of year for those celebrating their birthdays in England, which has gone back into lockdown for the third time.
"Thank you for your kind wishes on The Duchess' birthday," they wrote on the Kensington Royal account.