The 40-year-old actor confirmed in an Instagram Stories video Sunday that he accidentally took a plunge after attending the 2018 Golden Globe Awards ceremony.
Ventimiglia, who wore glasses and appeared to have wet hair, congratulated his "This is Us" co-star Sterling K. Brown on winning Best Actor in a Television Series - Drama before confessing he fell in a pool.
"Good time at the Globes tonight," he said. "I'm back home, I'm studying for tomorrow. And yes, I fell in the pool."
E! News reported Ventimiglia attended the HBO after-party at Circa 55 in The Beverly Hilton.
NPR critic Eric Deggans had tweeted that he thought he saw Ventimiglia slip and fall into the hotel's pool.
"At HBO's Golden Globes party. Believe I just saw Milo Ventimiglia from This Is Us slip and fall into the pool, which is mostly covered but open in one spot," he wrote.
Ventimiglia and Brown play Jack and Randall Pearson on "This is Us," which returns from midseason break Tuesday.
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Brown is the first African-American actor to win a Golden Globe award for Best Actor in a Television Series - Drama.
"You wrote a role for a black man that could only be played by a black man, and what I appreciate so much about this thing is I'm being seen for who I am and being appreciated for who I am," he said, thanking "This is Us" creator Dan Fogelman in his acceptance speech.
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