By Mark Abrams

PHILADELPHIA (CBS) – Oscar buzz surrounds the movie, Lincoln, and the recent National Geographic movie, Killing Lincoln, brought the television channel its largest audience ever for a single program.

Now, a recently-discovered, unpublished Lincoln family letter written nearly a year before his assassination is being made available by a Philadelphia-based historic documents dealer.

Nathan Raab of the Raab Collection, says the letter was written by Mary Todd Lincoln, the First Lady, on April 18, 1864, requesting babysitting services.

“It’s sort of odd to think of them writing a Treasury Department official asking Lincoln’s footman to come, essentially his body guard, to come babysit one of their young children. But that’s what happened here. And, in fact, he often babysat for young Tad.”

Tad was 11 at the time, Raab says, and the body guard, identified as Charles Forbes, had become a trusted family aide.

But Raab says Mrs. Lincoln’s plan to leave with her husband to attend an event in Baltimore later that day didn’t work out.

It was the same Forbes, history shows, who let the famous actor John Wilkes Booth into the president’s box at Ford’s Theater where Booth fatally shot the Lincoln in April 1865.

For more information on the Lincoln letter, click here.