Dr Harry Stopes-Roe, son of birth control pioneer Marie Stopes is now selling the letters he so treasured as a child.
The notes were penned 70 years ago by Pooh illustrator E H Shepard in reply to party invitations to the fictional bear.
They are littered with misspellings, to make them authentic, and drawings of Pooh and his friends.
Dr Harry Stopes-Roe, son of birth control pioneer Marie Stopes is now selling the letters he so treasured as a child.
The illustrator was a close friend of his mother and he would invite him and the bear to parties.
Buffkins
He said: "Quite often Shepard came, but when he did not come he sent those letters."
Both letters, which go on sale at Christie's auction house on 14 June, are addressed to "Buffkins", as Dr Stopes-Roe was known as a child.
The first, written in 1930 and including Pooh's misspellings, reads: "We are so sory that we cant come to yuor party."
The second reads: "I am very sorry that I canot come to your party. I love Punch and Judy but I am rather frigtned but it would be all rite siting near you.
"Love from Pooh."
Dr Stopes Roe, a retired lecturer and vice-president of the British Humanist Association, said: "Having thought about them and realised how valuable they were, now seemed to be a suitable time to sell them."
A third letter has been given to the British Library's archive along with four plasticine figures of Pooh and his friends.
Shepard, who died in 1976, was an illustrator for Punch magazine for 50 years, though he remains best known for his Pooh illustrations.