Newyddion gwych
Here's a breakdown:
* Newyddion: This means "news."
* Gwych: This means "great" or "excellent."
You can also say:
* Mae hyn yn newyddion gwych! (This is great news!)
* Newyddion da iawn! (Very good news!)
The choice of phrase might depend on the specific context and how much emphasis you want to put on the "greatness" of the news.