How to share news of my engagement with my grandparents while making sure they don’t tell my dad (their son) who I don’t want involved?

I’m very close to my paternal grandparents. Unfortunately, my dad (their son) is not as high on my list of people. He’s been absent for a large amount of my adult life, never reaches out, and most of my memories are of him being mentally and emotionally abusive to my mom.

My grandparents still keep in touch with him because he’s still their son, even though they support the rest of our family and are ashamed of some of the things he’s done.

How can I share something like an engagement with the grandparents I love while making sure my dad isn’t told too much? I don’t want him involved at all, but I also don’t want to hurt my grandparents by phrasing things the wrong way.
How to share news of my engagement with my grandparents while making sure they don’t tell my dad (their son) who I don’t want involved?
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