In addition to the personal papers bequeathed to Hebrew University when he died in 1955, Albert Einstein had some personal correspondance that were kept by his step-daughter Margot Einstein. Those were also given to Hebrew University on Margot Einstein's death in 1986, under the condition that they be sealed for 20 years.
The newly released papers showed a rather darker side of the genius than one would have guessed from the childlike picture of him sticking out his tongue. In fact, big Al seemed to be quite the womanizer--all while his family has full knowledge of the fact. For example, he wrote to Margot in 1931 about Ethel Michanowski, who followed him to Oxford:
"It is true that M. followed me and her chasing after me is getting out of control, I will tell her that she should vanish immediately. . . . Out of all the dames, I am in fact attached only to Mrs L. who is absolutely harmless and decent, and even with this there is no danger to the divine world order."To his second wife Elsa, he wrote this:
"Mrs. M. definitely acted according to the best Christian-Jewish ethics: 1) one should do what one enjoys and what won't harm anyone else; and 2) one should refrain from doing things one does not take delight in and which annoy another person. Because of 1) she came with me, and because of 2) she didn't tell you a word. Isn't that irreproachable?"
The letters revealed also items beyond just romantic entanglements; it showed Einstein's concern for his sons with Mileva: the broken relationship between his sons and him certainly troubled him greatly, especially after the older, Hans Albert, at 11 years old, told him off when he tried to invite Hans for a holiday trip because "if you're so unfriendly to [mother], I don't want to go with you either." There's also the issue of financial problems: the investment Albert made with his Nobel prize money sort of just went *poof* when the great depression hit.