(CNN) -- "The Berenstain Bears'" co-creator Jan Berenstain has died at the age of 88, according to a Facebook page dedicated to the furry characters Berenstain and her husband created.
"It is with very sad hearts we inform you that our dear Jan died on Friday, February 24. We are grateful for all of your very kind thoughts. Please remember her family at this very difficult time," said a statement on the Berenstain Bears Facebook page.
Berenstain and her husband, Stan, were already successful cartoonists when they decided to transition to writing children's books.
According to publisher Harper Collins, "The Big Honey Hunt," published in 1962, was the first book starring the bear family.
Since that time, more than 330 "Berenstain Bears" books have been published over the past 50 years, the publisher said.
More than 260 million copies have been sold, making it one of the best-selling children's book series in history, Harper Collins said.
The Berenstain Bears stories were so popular that the storyline was made into an animated TV show special on NBC in 1979 and then a hit daily TV series that began on PBS in 2002.
After Stan Berenstain died at age 82 in 2005, Jan Berenstain and her son Mike continued to write and illustrate new adventures for the Berenstain Bears, according to the Berenstain Bear Facebook page.
Berenstain lived in Bucks County, Pennsylvania, according to her publisher.