Ethel Michanowski was involved with Einstein in the late 1920s and early 30s, going so far as to chase him to England, said Barbara Wolff of the Hebrew University's Albert Einstein Archives, which on Monday unsealed more than 3,500 pages of correspondence written between 1912 and 1955, the year Einstein died at age 76.
Wolff described their relationship as an affair, but disclosed little about Michanowski other than that she was about 15 years younger than Einstein and was friendly with his stepdaughters.
Among the other revelations: Einstein lost much of his Nobel Prize money in the Great Depression, was a more devoted father than previously thought and made no bones about discussing his romantic liaisons with his second wife.
Einstein is known to have had a dozen lovers, two of whom he married, Wolff said.
Most striking about the more than 1,300 newly released letters was the way Einstein discussed his extramarital affairs with his second wife, Elsa, and his stepdaughter, Margot, the archivists said.
Michanowski is mentioned in three of the newly unsealed letters.
In a letter to Margot Einstein in 1931, Einstein complained that "Mrs. M." — Michanowski — "followed me (to England), and her chasing me is getting out of control."
Einstein was a founder of the Hebrew University and left it his literary estate and personal papers.
The letters — most of them to Elsa, and from his first wife and their two sons — have been in the Einstein Archives for years. But under the terms of stepdaughter Margot's will, they could not be made public until this July — 20 years after Margot's death, the university said.
This apparently will be the last time the public will receive such a large number of documents on Einstein, said Professor Hanoch Gutfreund, a former Hebrew University president and physicist.