Congratulations are in order for Kate Middleton, who's pregnant with her and husband Prince William's third child!

“It’s official! She is due on Christmas. Kate and William are overjoyed,” an insider tells Life & Style about the couple's baby news.

RELATED: Pregnant Peta Murgatroyd Bares Her Baby Bump in a Bikini!

The royals, who are already parents to son George, 2, and daughter Charlotte, 14 months, recently told Queen Elizabeth, who called the exciting news "a fabulous present for her 90th birthday this year."

william kate george charlotte getty images

According to the source, Kate and William want at least four children to follow in the monarch's footsteps (she has one daughter and three sons, including heir apparent, Prince Charles).

"They don’t mind whether No. 3 is a boy or a girl. They already have one of each, so they just want their next child to be healthy," the insider shares.

For more info on the royal pregnancy, pick up the latest issue of Life & Style, on newsstands now!

las 7/25 cover

And for a look at Kate's best maternity style, scroll through the gallery below!