The Hollywood stars were inside the Four Seasons Hotel to promote their upcoming film, The Ugly Truth, when they were forced to evacuate, along with 400 other guests.
Heigl and Butler were left waiting outside the luxury complex while police investigated the premises after a phone call warned of a nearby bomb, according to People.com.
The Scottish actor was seen posing for pictures with members of the AC Milan soccer team, who were in the city to play a game against Los Angeles Galaxy on Sunday night.
Cops found no unattended packages or luggage and the hotel reopened two hours later.
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