Princess Charlene of Monaco, married to Albert II since 2011, is pregnant with twins, a source confirms to Us Weekly Credit: Valery Hache/AFP/Getty Images

Double royal trouble! Princess Charlene of Monaco is pregnant with twins, a source confirms to Us Weekly.

The mom-to-be and her husband Prince Albert II announced in May that they were first expecting. "The birth is expected at the end of the year," the couple told Us in a statement at the time.

Princess Charlene, 36, and 56-year-old Albert II — the son of Rainier III, Prince of Monaco and the late legend Grace Kelly — first met in 2000 during a swimming competition. The royal couple later tied the knot in Monaco in July 2011.

Albert II discussed his wife's pregnancy at the opening of the new Monaco Yacht Club in June. "[We're] taking every cautious step to make sure everything goes well," he said, via Daily Mail. He added to the Associated Press that the pair were "overjoyed" and "thrilled" about the next chapter.

The twins will be the first children for Princess Charlene (maiden name: Wittstock). She showed off her growing baby bump at the Seventh Annual World Focus on Autism event in NYC on Sept. 25. Albert II is already dad to Jazmin Grace Grimaldi, 22, and Alexandre Coste, 10, whom he had in previous relationships.