To not know what to do!!

[Trappedmumof3]

To cut a very long story short, I recently found out via a DNA test that my Dad was not my biological father. The test gave me the name of my actual biological father, who lives in Australia and must be in his late 60s or 70s. He was a sperm donor in the mid 1970s for a fertility hospital in London that my parents went to. He must have registered his details on the ancestry.com website and done a DNA test for his name to have come up as a 100% guaranteed link to me.

I have no desire to contact him to establish a relationship or anything like that, but I feel that he might be pleased to hear that his 'donation' resulted in a child and made my parents very happy.

What would you do? Contact him or leave well alone?? I just can't decide!!

Thanks

Thanks for the answers. I like to hear other people's opinions on things. It helps to try to get my perspective right!
My parents had fertility issues and adopted 2 children. Tragically one of them died when he was 5. Technology had moved on a bit by then and they were given fertility treatment and had me and my brother. We grew up knowing all of that but a couple of years ago Mum told me that the fertility treatment basically involved mixing Dad's (badly swimming) sperm and mixing it with that of a donor. I did a DNA test out of curiosity and ended up with the name of my biological father, which is an unusual name, so I googled him and found out a few things about him - mainly that he was a medical student in London in the 1970s and that he now lives in Australia. There are no half siblings of mine listed on the ancestry website, but there are a few distant cousins.
I have no desire to meet him or want any involvement from him, I just would like him to know that his - er - donation brought about a lot of happiness! But I don't know if that's a terrible idea or not, so I thought I'd come on here! My friends say I should do it but I have my doubts! Thanks all!