Marshall, known for shows like "Happy Days" and romantic comedies like "Pretty Woman" and "Valentines Day", died on Tuesday at the age of 81.
"... Garry was goodness itself. He was generous. He was kind beyond kind. He was thoughtful and sweet and so funny you would pee yourself a little," the actress recalled in a Facebook post.
Hathaway, who played Mia Thermopolis in the movie, says she is happy that when they last met Marshall blessed her yet-to-be born son.
"Before we made the Princess Diaries, he told me 'You never know if a movie is going to be a hit or not. The only thing you can control is the memories you make when shooting it. So, let's make some good memories."
"You don't meet a lot of people that kind of courageous nowadays. I couldn't see it when he was right in front of me, but I see him so clearly now that he has moved on- Garry was a Hero. Not a run-into-a-burning-building-to-save-a-hampster hero per se, but he looked on the bright side of every situation and was unfailingly warm and loving to everyone he met.