During her employment with Piper, according to courtier count Lars von Engeström, she was "a little girl, and everyone laughed at her because she was in love with Duke Frederik.

"[2] She ended her employment at Piper and entered into a relationship with a young merchant, and brewer, who supported her financially and paid for her education at a sewing school.

On 2 January 1780, she was presented at the royal court at Gripsholm Castle as the official lover of Frederick Adolf by permission of king Gustav III of Sweden.

The ladies of the Crown Prince, initially somewhat scandalised over this visit, soon found themselves content and spoke much to the advantage of Mamsell Hagman.

Sophie Hagman appeared openly with the prince at court, which together with Hedvig Taube made her one of only two official royal mistresses in the history of Sweden.

[3] The Poet Bellman called her an image of beauty: "Her entire being was a fest to my eyes", and the King once embraced her as a sister-in-law at Gripsholm Castle.

Eventually, even Count Axel von Fersen the Elder, known as a strict moralist and highly disproving of all extramarital sexuality, acknowledges her quality and admitted that she had made a good impression on everyone.

In 1780, the relationship was temporarily broken because of Frederick Adolf's infatuation and marriage plans to Countess Margareta Lovisa Wrangel.

Sophie Hagman was met with great sympathy at court because of the good impression she had made and because she was now without means to support herself, and Gustav III therefore promised her a pension.

[2] When the marriage negotiations with Wrangel failed and the Frederick Adolf lost interested in her in 1781, he returned to Hagman and resumed the relationship with her.

[2] In 1784, Axel von Fersen the Elder reported that Prince Frederick Adolf lived a quite private life with Sophie Hagman in a circle of close friends, and in 1786, Princess Hedvig Elisabeth Charlotte confirms that the prince isolated himself with Hagman at his estate, completely taken by her beauty.

The gentlemen counted themselves lucky if the gave them but a minute"; she handled her role as a hostess: "Not with the arrogant pride of a Princess, but with the natural politeness of the middle class.

During the Russo-Swedish War (1788–1790), Frederick Adolf came in conflict with the King, refused to serve under his brother Charles and left the army in December 1788.

Frederick Adolf replaced her with the actress Euphrosyne Löf, while Sophie Hagman entered into a relationship with the singer and composer Edvard du Puy.

The first time, she was in the company of a "Mrs Jouffrouy", the wife of Prince Frederick Adolf's economy minister, and met the poet and bishop Franz Michael Franzén, who wrote a description of their encounter.

At this point, she apparently had the responsibility of her brother's children, as she told Franzén that she contemplated to arrange a place for her nephew on an East India ship, but there are no more information of that.

In 1796 and 1802, she made pleasure trips to Paris under the name "Madame Hedengrahn" in the company of Captain Carl Christian Ehrenhoff.

[2] Sophie Hagman lived the last years of her life "admired for her still preserved beauty, her lovable, pleasant being and her good heart", and was a popular hostess, giving small balls and suppers for people such as the sculptor Johan Tobias Sergel.

[2] Sophie Hagman died in 1826 and willed her property to her sister's children and to her close friend Jeanette Stenström.