Write an e-mail to your boss using the below stated lines:
Learnt that boss is taking up a new project- planned for investment of millions of dollars in it- unfortunately plan will not work- competitor has similar project- this project was a failure- no demand in the market- hence should stop this idea immediately.
I have learnt that you are taking up a new project and planned for investment of millions of dollars in it. Unfortunately, the plan will not work since our competitor has a similar project. Moreover, this project was a failure and there is no demand in the market. Hence , it is better you should stop this idea immediately.
Thanks & regards,