Lost In The Post

lA Corkman sent his son to University and a few days later received a letter from him asking for £10. To save face he added the following P.S.:
'I am so ashamed to ask you for money that I have run after the postman to recover this letter but the post had already gone. I can only pray that the letter will be lost in the post'. A few days later he received the following letter from his father.
Dear Son,
Don't upset yourself, the letter was lost in the post.
Your loving father.
P.S. I would enclose the £10 but I have already sealed the envelope.