"Even though Betty was about to be 100, I thought she would live forever," Witjas said in a statement.
"I will miss her terribly and so will the animal world that she loved so much. I don't think Betty ever feared passing because she always wanted to be with her most beloved husband, Allen Ludden. She believed she would be with him again."
Stars such as Ryan Reynolds, US president Jo Biden, Reese Witherspoon, Viola Davis, Debra Messing, Ellen Degeneres and Diane Kruger paid their respects on social media following the loss.
Reynolds, who has been engaging in banter with White just days prior, posted a picture to his Instagram of the actress, who Reynolds had previously teased was his
"ex-girlfriend".
The iconic actress previously responded in an interview with People Magazine, saying, "I've heard Ryan can't get over his thing for me, but Robert Redford is The One."
Reynolds tribute following the news read: "The world looks different now. She was great at defying expectations. She managed to grow very old and somehow, not old enough. We'll miss you, Betty.'
Star Trek actor George Takei wrote: "Our national treasure, Betty White, has passed just before her 100th birthday. Our Sue Ann Nivens, our beloved Rose Nylund, has joined the heavens to delight the stars with her inimitable style, humour, and charm. A great loss to us all. We shall miss her dearly."
Late-night talk show host Seth Meyers added his memory of White, sharing a story about her SNL performance and aftermath.
"RIP Betty White, the only SNL host I ever saw get a standing ovation at the after-party. A party at which she ordered a vodka and a hotdog and stayed 'til the bitter end."
Talk show host and actress Ellen DeGeneres tweeted "What an exceptional life. I'm grateful for every second I got to spend with Betty White. Sending love to her family, friends and all of us."
US President Joe Biden paid tribute to beloved Golden Girls star calling her a "lovely lady".
He spoke to reporters after enjoying a New Year's Eve lunch: "That's a shame. She was a lovely lady - 99 years old," said the president when told of the actress's death. "As my mother would say, 'God love her.'"
Actress Jennifer Love Hewitt posted a video of herself crying with the message: "Heartbroken. My angel. My idol. My friend. I miss you already."
Oscar-nominated songwriter Diane Warren said: "A few years ago at an animal charity event I bid on a day at the zoo with Betty White. Not only was she a legend but a fierce advocate for animal rights. Both the humans and the animals are so sad today Betty."
Singer Lizzo tweeted a simple broken heart next to the name Betty, sharing the mood of many.
Bravo star Andy Cohen tweeted: "Tonight we will raise MANY glasses to the WONDERFUL legacy of Betty White!!!'
Actress Ariana DeBose tweeted: "So we're eating cheesecake in honour of Betty White. Who's with me?"
The Golden Girls star - who was born in 1922 - was a pioneer of early television with a career spanning nine decades.
White began her television career as a $50-a-week sidekick to a local Los Angeles TV personality in 1949. She was hired for a local daytime show starring Al Jarvis, the best-known disc jockey in Los Angeles.
The comedic actress went on to have a vast career in the entertainment industry, as well as being one of the first women to produce a sitcom, Life with Elizabeth, which saw her named honorary Mayor of Hollywood.
White is also widely known for her roles as Sue Ann Nivens, as a man-crazy TV hostess on the sitcom The Mary Tyler Moore Show, Rose Nylund on The Golden Girls and Elka Ostrovsky on the sitcom Hot in Cleveland.
Her youthful and cheeky humour saw even smaller roles, such as her part in the comedy The Proposal propel her further into stardom with her unique brand of salty language and killer one-liners.
White grew to become a beloved symbol for all generations, and a role model for how to grow old joyously.
