Hundreds of celebrities have already paid their respects to one of Hollywood's most famous actors, Robin Williams, but one former actress who worked with Williams on "Mrs. Doubtfire" recently penned what could be the most touching letter yet.

Wilson, who gained popularity after starring in the '90s film "Matilda," was blessed with the chance to work with Williams, as the late actor's youngest daughter in the classic 1993 comedy "Mrs. Doubtfire."

At that time, Wilson was only six years old and now, at 27, after officially retiring from show business, Wilson dished via her personal blog everything she could possibly remember about her on-screen father, according to People.

"Robin Williams, as I knew him, was warm, gentle, expressive, nurturing and brilliant. While it can be hard for me to remember filming Doubtfire, I've been flooded with memories in the past few days. It's humbling to know I am one of the few people who was there for these moments, that he's no longer around to share them," Wilson wrote.

Wilson also recounted the last time she saw her on-screen father while he was filming "August Rush" in Washington Square Park.

"He told me how grown-up I looked and asked how I like NYU. It was small talk, but something about the way Robin looked at me made me feel like he truly cared. This was someone for whom everything mattered," she wrote.

Wilson opened up about her regret for not being able to explain to Williams in person what she meant when she said she could no longer revisit her role on "Mrs. Doubtfire," the NY Daily News noted.

"I had thought maybe the next time I saw Robin I would explain myself to him, let him know that I had loved working with him but didn't feel like we could do it again, and that being in major studio films again meant a level of scrutiny I didn't think I could deal with. I wanted to apologize and know he understood. It hurts to know I can't."