Former Delaware Attorney General Beau Biden, Vice President Joe Biden's son, is being treated at a military hospital outside Washington, the vice president's office said.

The vice president's older son is being treated at Walter Reed Medical Center in Bethesda, Md., the office said. No reason was given, but CNN quoted an unnamed source calling the situation "serious." Beau Biden is running next year to be Delaware's governor.

In 2010, Beau Biden suffered a mild stroke. Three years later, he underwent surgery after being diagnosed with a brain lesion.

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