Millions of people are sharing their fond memories of the late Robin Williams, who tragically passed away yesterday. Among those paying tribute was Norm MacDonald, who told an almost-unbelievable tale involving Robin.

In a series of tweets, each punctuated with "#RIPRobinWilliams," MacDonald told the story of his first time on David Letterman's show. Robin Williams was also on the show that night, which only made Norm's anxiety worse. 

Norm was talking to a friend on the phone in his dressing room and describing the situation when Robin walked by. Norm told his friend what just happened, and Robin overheard his name – so he decided to drop in for a visit. 

What followed was a legendary half hour of Norm's life with Robin Williams, who also took his phone from him and took his friend's Chinese takeout order and tied Norm's tie in a windsor knot. You can read the entire story on his Twitter feed.

Below is a collection of other celebrities paying tribute to the late Robin Williams. You will be missed, Robin.