A long-forgotten collection of never-before-seen modern Indian art, including unpublished artworks by master artists V.S. Gaitonde and Ram Kumar, will go under the hammer for the first time at Sotheby's in London on September 29, the auction house announced on Wednesday.

Assembled by Gunnar Hansen and his wife Inger almost half a century ago, the history of this collection is closely tied to that of one of India's most influential businesses of the 20th century, Larsen & Toubro, for whom Gunnar worked for over 20 years.

While helping to make L&T the company it is today, Hansen also made a life for himself and his family in India. Hansen and his wife, Inger, moved from Denmark to India in 1953, and it was in Bombay they acquired their passion for modern Indian painting. As per Sotheby's, the family were regular visitors to Gallery Chemould and Pundole Art Gallery, where they met the great Indian modernists and amassed their superb collection.

According to Ishrat Kanga, Head of Sotheby's London Modern & Contemporary South Asian Art Sale, the collection is a "true hidden gem".

"All of the paintings offered here have rarely been seen in public, if ever, before. The pieces were acquired by the Hansens in India in the 1960s and 1970s, soon after leaving the artist's studios and have been treasured by the family for some 40 to 50 years. Enthused by the radical art they discovered in post-independence India, the Hansens assembled a visionary collection that today is a perfect time capsule, demonstrating the depth and quality of abstract and non-objective art which was being created in India at this extraordinary moment in time."

One of their first purchases was an exquisite red, orange, black and ochre Untitled canvas by V.S. Gaitonde, estimated at e1.5 – 2 million (roughly Rs 14 crore- Rs 19 crore), which Hansen bought after "test driving" it for a few days in his house as a loan in 1969 before making the purchase. Another is a Ram Kumar painting from the same year, hung in their dining room. The painting is accompanied by a personal letter from the artist in which he asks for copies of a greeting card Hansen had produced with the image of the work.

Other important artists represented in the Hansen collection include Krishen Khanna, Mohan Samant and Piraji Sagara, and are offered alongside long-overlooked artists that will be offered in a Sotheby's sale for the first time: Nareen Nath, Triloke Kaul, Homi B. Patel, S.R. Bhusan and Sanat Thaker. The collection includes 18 works in total by 15 different artists and is estimated at e1,799,000 – 2,401,000, where the upper estimate translates to almost Rs 23 crore. The sale also offers a selection of works from the estates of Bhupen Khakhar and Patwant Singh.

The sale will be on public exhibition from September 25-29 at Sotheby's London..