Kate Middleton and Prince William are thrilled by the arrival of Prince Harry and Meghan Markle's second child.

The Duke and Duchess of Cambridge congratulated the couple on social media.

Baby Lilibet 'Lili' Diana Mountbatten-Windsor was born on June 4 in Santa Barbara, CA.

The Queen, Prince of Wales, and Duchess of Cornwall have also been informed and are delighted with the news.

Lili's first name honors the Queen, whose family nickname is Lilibet.

Her middle name, Diana, is in honor of the Princess of Wales.

The couple announced the birth officially.

The trusted care of the doctors and staff at Santa Barbara Cottage Hospital delivered Lili.

The Cambridges shared their excitement and best wishes for the family.