How do i make tkinter messagebox pop after an if statement is met? how do I make the program constantly check if somebody has won.?

Question

I am making a tic tac toe game, and I would like for the message box to pop up when the win condition has been met. But right now I have to click an additional time before the message box opens. how do I make the message box open without having to make the user click again?

basically

if X wins the tic tac toe game , I want the messagebox to pop up, but currently I have to click 1 more time . how do I make the program constantly check if somebody has won.