Swedish royal Princess Madeleine is a mom of three.
"HRH Princess Madeleine gave birth to a healthy child at Danderyd Hospital on Friday, March 9, 2018 at 00.41. Both mother and child are doing well," the post reads.
Princess Madeleine and O'Neill are expected to announce their daughter's name next week. The couple already share 4-year-old daughter Princess Leonore and 2-year-old son Prince Nicolas.
"We are delighted with the new addition to our family," O'Neill said in a statement, according to People.
"Leonore and Nicolas have their long-awaited sibling," he added. "They can't wait to meet their new baby sister."
Princess Madeleine is the youngest of King Carl XVI Gustaf and Queen Silvia's three children.
The monarchs are returning home from a vacation in the Swiss Alps to celebrate their new granddaughter's arrival.
"The King and Queen are heading home to Sweden right now," palace rep Margareta Thorgren said.
The Swedish Royal Court/Instagram