Nurse turned billionaire: Subway heiress is one of the biggest philanthropists you've never heard of.

The University of Connecticut has announced its largest donation, totaling $40 million, to build a new medical school building.

The donor is Elizabeth DeLuca, the 76-year-old widow of Subway chain pine tree Fred DeLuca, who died of leukemia in 2015. Elizabeth DeLuca, a former nurse, and her son Jonathan inherited a fortune that includes a stake in the business and billions in cash.

Then, just six weeks before her record-breaking donation to the University of Connecticut was revealed, she and the family of deceased Subway partner Peter Buck agreed to sell the fast-food chain to private equity firm Roark Capital for $9.7 billion, bringing her family another nearly''3.4 billion in cash.

Elizabeth DeLuca is one of the richest women in the world, with an estimated fortune of 8.2 billion dollars. However, she is far from being a famous person and there are only a few pictures of her posted on the internet.

The DeLucas have also donated 27,000 acres of land in Florida to the University of Florida. The land, known as the DeLuca Preserve, is used as a "living classroom and laboratory" for students and researchers at the university.

Elizabeth DeLuca has also donated more than $100 million to''supporting education and youth groups in Florida and Connecticut.