From Wikipedia:

Livia Orestilla, or Cornelia Orestilla [1] was a Roman Empress as the second wife of the Emperor Caligula in AD 37 or 38. She was originally married to Gaius Calpurnius Piso (in particular the one involved in a conspiracy overthrow the Emperor Nero in AD 65),[1][2] who was persuaded or forced to annul the marriage so that Caligula could marry her. According to both Dio and Suetonius, this occurred during the wedding celebrations. Suetonius claims that Caligula issued a proclamation the next day that he had acquired a new wife in the tradition of Romulus and Augustus, who had both stolen wives from other men. Days later he divorced her and two years later banished her on suspicion of returning to her other husband.

Citations

1. a b Dio, Book 59 Ch. 8.7
2. Suetonius, 25.1

References ++

• Suetonius, Life of Caligula
• Dio, Roman History