The daughter of Prince Andrew and Sarah Ferguson announced the news via Buckingham Palace and her own personal Instagram account.
The baby, whose gender has not been shared, is due this summer and will join their almost 2-year-old son, August.
"The family are delighted and August is very much looking forward to being a big brother," the Palace said in a statement.
Eugenie also shared the news on her own personal Instagram account, writing, "We're so excited to share that there will be a new addition to our family this summer."
In the sunset pic, a smiling Eugenie gets a hug from August, who appears to be kissing her stomach. The pic was snapped by her husband, Jack.
August's grandmother was also thrilled over the baby news. "You will be sharing puddles, Augie ! Superb news, Granny heaven…. So deeply grateful," the Duchess of York captioned a photo of her grandson in the rain.
August was born in February 2021, and appeared at the Platinum Jubilee of his late great grandmother, Queen Elizabeth II, in June 2022. At the time, Eugenie shared several photos of her little guy waving at the crowds and the airplane flyover.