Feb. 13 (UPI) -- A powder substance found in a letter that sent President Donald Trump's daughter-in-law and mother in-law to the hospital, as a precaution, was found to be cornstarch.
The letter was addressed to Donald Trump Jr., the president's eldest son, and sent to the house of his mother-in-law, Bonnie Haydon -- who passed the envelope to her daughter, Vanessa Trump.
All three who were exposed to the cornstarch are expected to be fine, the New York Police Department said.
Donald Trump Jr., called the letter "disgusting" in a tweet Monday.
"Thankful that Vanessa & my children are safe and unharmed after the incredibly scary situation that occurred this morning," he wrote. "Truly disgusting that certain individuals choose to express their opposing views with such disturbing behavior."
Vanessa Trump thanked the NYPD, the Secret Service and the Federal Bureau of Investigation on Twitter for making sure she was safe.
Ivanka Trump also acknowledged the incident.
"Wishing I was by her side today. No one deserves to be frightened this way. There is no excuse," she tweeted.
The U.S. Secret Service said it's investigating the incident.