Williams sent "love" to the New Zealand-based fan Vivian, whose bucket list included meeting the 'Good Will Hunting' star before she died.
Vivian is currently still suffering from lung, bowel and liver cancer, which she was diagnosed with in January.
Williams committed suicide on August 11 at age 63 and was in the early stages of Parkinson's disease, according to his wife.
"Sending all my love to you, Jack and Sophie," Williams tells Vivian in the video, referring to her husband and their one-year-old daughter.
"Mark this off your bucket list. What's going on? It's all right, it's all right, it's all right. I'm just channeling Matthew McConaughey. Much love to you, baby," he said in the video, before concluding by blowing a kiss to Vivian.