Shattered! Billie Lourd Mourns Mom Carrie Fisher In Heartbreaking Throwback Photo

Billie Lourd took to Instagram on Wednesday to honor her mother, Carrie Fisher, posting a touching throwback photo of the pair.

"'If my life weren’t funny then it would just be true and that is unacceptable,'" she wrote, quoting her famous mother.

Then, in her own words, Lourd shared: "Finding the funny might take a while but I learned from the best and her voice will forever be in my head and in my heart."

As RadarOnline.com readers know, Fisher suffered a massive heart attack on a United Airlines flight from London to Los Angeles, eventually losing her life on Tuesday. She was only 60.

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Just two days later, Fisher's mother and Lourd's grandmother, Debbie Reynolds, died from a series of strokes.

In the wake of her mother and grandmother's deaths, Lourd has been spotted spending ample time with boyfriend Taylor Lautner, who sources tell PEOPLE "has really been there for Billie."