Thea Oljelund (1921–2012 ) was a Swedish writer who wrote a pony book for the Stabenfeldt imprint. She has written very much more in her native Swedish, but nothing as yet that has been translated into English.
She was a feisty child who was bullied at school, and left early. Her father’s library provided much fodder for her. She read his copies of Ulysses, The Three Musketeers and Strindberg amongst much else: in the 1920s there were not many children’s books available in Swedish. Her early efforts in writing were on her father’s typewriter; they bore fruit, as she worked as a journalist. For 40 years she worked with the Åhlén och Åkerlands Press. She wrote around 70 books: crime books for the adult market as well as many children’s books. Her longest series is the 24-book Pirkko series, which is about horses. As far as I am aware, Summer with Prince is part of a four-book series, only one of which has been translated into English.
Finding the book
Very tricky to find in the UK, but widely available in the USA.
Bibliography: pony books only
Summer with Prince, Stabenfeldt, 2007, pb