The 41-year-old actress was especially close to Alan, given that he was her former father-in-law. Paula married the Growing Pains star's son, singer Robin Thicke, in 2005 -- after the two had dated since their teenage years -- though they separated in February 2014 after 21 years together.
"I knew Alan since I was 15 years old and he had a tremendous effect on my life," Paula Instagrammed on Tuesday alongside a picture of a smiling Alan. "I loved and respected him so much! So many great memories and laughs together. We will miss him so much! His grandson is quite sure he is still here with us in spirit."
And although Paula and Robin have moved on since their breakup, the Mission: Impossible - Ghost Protocol actress has no hard feelings towards her ex. Earlier this year, she shared a sweet throwback of the two together in their younger years.
"My friend showed me this and it took my breath away," Paula wrote. "We were babies and we had a beautiful baby. What an amazing time in my life. No regrets! Celebrating this amazing life we get to live never knowing what's coming next. Love is always the answer."
Robin hosted a star-studded memorial to his father on Sunday, who died at age 69 after suffering a heart attack while playing hockey at a skating rink in Burbank, California. A source told ET that about 150 people attended the emotional memorial service that took place at Alan's ranch in Carpinteria, California, including Leonardo DiCaprio, Bob Saget, Kevin Costner, and the entire cast of Growing Pains.
A source close to the family previously told ET that Robin "really stepped up" in planning his father’s memorial.
"[Robin's] realized that he has to be incredibly strong for his family right now," the source said. "He is focused on honoring his dad, and making this easy on his family."