Irish children’s author Sam McBratney, most widely known for the classic, bestselling picture book Guess How Much I Love You, died September 18. He was 77.

McBratney was born March 1, 1943 in Belfast, Northern Ireland and grew up in the nearby town of Lisburn. He graduated from Trinity College in Dublin with honors and a degree in modern history and political science. He married his wife Maralyn in 1964, and while they were raising their three children, McBratney earned his living as a primary and secondary teacher of history and English.

By 1976 he had published his first book, a novel entitled Mark Time, about rival gangs of preteen boys, one Catholic, one Protestant, set during the Troubles in Northern Ireland. He continued writing and publishing children’s books on the side until the publication of Guess How Much I Love You in 1994. The enormous success of the gentle bedtime tale illustrated by Anita Jeram, in which Little Nutbrown Hare and his father, Big Nutbrown Hare, try to top each other in expressing who loves the other more (e.g. “I love you right up to the moon,”/…“I love you right up to the moon—and back”), marked McBratney’s professional shift to full-time author.

Though McBratney created more than 50 books during his career, Guess How Much I Love You has stood apart over the years, selling more than 50 million copies worldwide. It has been translated into 57 languages and is at the heart of a global licensing program. A highly anticipated companion book, Will You Be My Friend?, also illustrated by Jeram, has a global pub date of September 29. Sharing some insight on his approach to the new work, McBratney recently said, “When writing about the hares, I aim to describe moments of emotional significance but with loads of humor and the lightest of touches. This story is about one of those moments. Little Nutbrown Hare’s world suddenly glows with the discovery of friendship.”

In a statement, Karen Lotz, group managing director of the Walker Books Group in the U.K. and president and publisher of Candlewick Press in the U.S., paid tribute to the author. “Sam McBratney was a profoundly lovely human being,” she said. “You could recognize his voice in a moment—he was an exceptionally talented wordsmith and always knew exactly what children would enjoy hearing the most. Amazingly humble, he also was a hilarious storyteller and convivial companion. We never had better days than when he would come down from Ireland to visit the offices in London. Our world dims with his passing, but his legacy of kindness and humor will burn bright and carry on across time and distance through his stories, which have touched the hearts of readers around the globe.”

And Donna Cassanova, character publisher of Walker Books, offered this remembrance: “I feel such great sorrow at the passing of my dear friend Sam, but also an immense sense of pride, and privilege, to have worked for so long with such a master of his craft. Through the years, as Guess How Much I Love You achieved great success and acclaim, Sam never failed to express his profound surprise at the power of the message within his text. The joy he felt at knowing so many people connected with the gentle celebration of unconditional love was ever palpable. It is also the true mark of the man that he never failed to recognize the role that Anita Jeram’s exquisite illustrations play in the success of Guess How Much I Love You. They were a literary pairing of the highest caliber. Sam faced everything in life, and death, with such great, good grace and humor. He always smiled out at the world, and I feel so lucky to have felt the warmth of his smile.”