With today marking the 15th anniversary of the devastating terrorist attack on the World Trade Center, numerous celebrities are taking to social media to pay their respects to those who died on that tragic day.

Nearly 3,000 people lost their lives when hijacked airliners flew into each of the Twin Towers on Sept. 11, 2001, with more than 6,000 injured.

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Here’s how celebs ranging from Cher to Kevin Hart to Lady Gaga and many more are honouring this somber anniversary.