A series of unpublished love letters from Mexican artist Frida Kahlo to her lover Jose Bartoli are expected to fetch upwards of $120,000 when the passionate missives go up for auction later this . During her marriage to muralist Diego Rivera, Frida penned the letters to Jose, a Catalan artist whom she met while she was recovering from surgery in New York. Their steamy correspondence began shortly after she returned to Mexico following the trip and continued throughout their secret three-year romance. 'I don’t know how to write love letters. But I wanted to tell you that my whole being opened for you,' then-39-year-old Frida wrote in October of 1946. Scroll down for video . Secret romance: Mexican artist Frida Kahlo (pictured) wrote passionate love letters to Jose Bartoli from 1946 and 1949 while she was married to muralist Diego Rivera . Enduring love: A collection of 25 of the unpublished letters will be auctioned off at Doyle New York on April 15 . She continued: 'Since I fell in love with you everything is transformed and is full of beauty… love is like an aroma, like a current, like rain.' The letters, 25 of which are headed to auction at Doyle New York on April 15, were written in Spanish between August 1946 and November 1949 and saved by Jose until his death in 1995. The archive of passionate messages, which comprise more than 100 pages, were passed down through different generations his family until they reached the current owner. According to Frida Kahlo biographer Hayden Herrera, the artist told Jose to sign his letters as 'Sonja' so that Diego would think they were from a woman if he came across them. High price: The letters (pictured) are expected to fetch upwards of $120,000 dollars . Pet names: Frida signed her letters to Jose 'Mara', which biographer Hayden Herrera explained is probably short for 'Maravillosa', a name Jose would call her . Creative couple: Jose, a Catalan artist, can be seen sitting at an easel as he works on a painting . Handle with care: This letter from the archive shows a stain on the right hand corner of the paper . Famous works: In this letter, Frida refers to 'Tree of Hope', a painting she created shortly after she met Jose . Diego, a muralist and a notorious Lothario, who once had an affair with Frida's younger sister Cristina, endured Frida's love affairs with women, but her relationships with other men would drive him to bouts of crazed jealousy. Meanwhile, Frida inscribed her letters with the name 'Mara', which Hayden explained is probably short for 'Maravillosa', a name Jose would call her. The collection also includes an original drawing of a sleeping cat, pressed flowers, ribbon, beads and drafts of a few of Jose's responses. Frida's candid messages to her lover shed light on her important paintings, an unknown pregnancy and her relationship with Diego, as well as her adoration for her Jose. Full package: The letters also include an original drawing of a sleeping cat and drafts of a few of Jose's responses . Sketch artist: Frida sent Jose this drawing of a tree in reference to 'The Tree of Life' City living: Frida posed for this photo in front of a skyline. She and Jose met when she was recovering from surgery in a hospital in New York . Long distance love: Frida ended this letter to Jose with a kiss, leaving behind a lipstick print of her mouth . Their secret affair began when Frida, who was left a partial cripple after a 1925 bus accident, was recovering from a spinal fusion performed in June, 1946 at New York’s Hospital for Special Surgery. Frida's sister Cristina was the one to introduce her to Jose, who moved to New York after fighting in the Spanish Civil War. They fell in love during his visits to the hospital and continued their long-distance courtship after she returned to Mexico. After Frida sold her 1946 painting Tree of Hope, which was inspired by her recent surgery, she wrote to Jose about his words influenced her creation. 'I remembered your last words and I began to paint,' she explained. 'I worked all morning and when I finished eating I kept on painting until there was no more light. But afterward I felt so tired and everything hurt.' An artist's life: Frida was photographed holding this statue while she stood in front of a blue cement wall . Inspired work: Frida sketched this drawing of a sleeping cat and sent it to Jose . Added images: This letter featured a picture of a women sleeping in a bed while another walked away . Last words: Frida ends this letter by telling Jose that she loves him . Epic romance: In this letter Frida told Jose she loves him the way that he is . In the painting one version of Frida lies in a hospital bed, while another depiction of herself sits proudly while holding a flag. While painting the piece, Frida inscribed 'Tree of Hope Keep Firm' a line of a song that she and Jose both liked. According to Hayden, Frida wrote in several of her letters to Jose that she had missed her period, in a way that suggested she was in some ways hoping to have his baby despite knowing it was nearly impossible because of her spinal injury. 'If I were not in the condition I am in now and if it were a reality, nothing in my life would give me more joy. Can you imagine a little Bartoli or a Mara?' she wrote. New images: Frida posed in her house for this photo take by French photographer Gisèle Freund . Full of life: Frida can be seen standing in her garden in Mexico in this image shot by Gisèle . Meta moment: Frida Kahlo and Dr Juan Farill were photographed in her home in 1951. In his photo, they are standing in front of one of her works in which she pictured herself painting Dr Farill's portrait .
The Mexican painter penned the letters to fellow artist Jose Bartoli from 1946 and 1949 while she was married to muralist Diego Rivera.
The 25 letters Jose had saved until his death in 1995 are headed to auction at Doyle New York on April 15 and expected sell upwards of $120,000.