Can't figure out how to setup GridPane at the start of my project without using button layout

I have trouble with adding Pane to GridPane without using a button(by clicking the button in fxml layout). How can I make my app add the squares(white and black table) to the screen from the start instead of waiting for user to click the button I added to layout?

App Class:

public class Application extends javafx.application.Application {

    @Override
    public void start(Stage stage) throws IOException {
        FXMLLoader fxmlLoader = new FXMLLoader(Application.class.getResource("main-view.fxml"));
        Scene scene = new Scene(fxmlLoader.load(), 800, 800);
        stage.setTitle("Chess #1!");
        stage.setScene(scene);
        stage.show();

    }

    public static void main(String[] args) {
        launch();
    }
}

Here is Controller code:

import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.Pane;

import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.ResourceBundle;

public class PrimaryController {

    @FXML
    private GridPane gameboard;

    @FXML
    private Button startButton;
    private Pane[][] paneArray;
    private List<Pane> paneList;

    @FXML
    public void start() {
        paneList = new ArrayList<>();
        paneArray = new Pane[8][8];
        for (int i = 0; i < 8; i++) {
            for (int j = 0; j < 8; j++) {
                Pane pane = new Pane();
                paneList.add(pane);
                paneArray[i][j] = pane;

                String black = "-fx-background-color: black;",
                        white = "-fx-background-color: white;";

                if (i % 2 == 0) {
                    if (j % 2 == 0) {
                        pane.setStyle(white);
                    } else {
                        pane.setStyle(black);
                    }
                } else {
                    if (j % 2 != 0) {
                        pane.setStyle(white);
                    } else {
                        pane.setStyle(black);
                    }
                }

                gameboard.add(pane, j, i);
            }
        }
    }
}

Here is fxml view:

<VBox alignment="CENTER" spacing="3.0" xmlns="http://javafx.com/javafx"
      xmlns:fx="http://javafx.com/fxml" fx:controller="com.kuraido.urslanchessengine.PrimaryController">
    <children>
        <GridPane fx:id="gameboard">
            <columnConstraints>
                <ColumnConstraints hgrow="SOMETIMES" prefWidth="100.0" />
                <ColumnConstraints hgrow="SOMETIMES" prefWidth="100.0" />
                <ColumnConstraints hgrow="SOMETIMES" prefWidth="100.0" />
                <ColumnConstraints hgrow="SOMETIMES" prefWidth="100.0" />
                <ColumnConstraints hgrow="SOMETIMES" prefWidth="100.0" />
                <ColumnConstraints hgrow="SOMETIMES" prefWidth="100.0" />
                <ColumnConstraints hgrow="SOMETIMES" prefWidth="100.0" />
            </columnConstraints>
            <rowConstraints>
                <RowConstraints prefHeight="100.0" vgrow="SOMETIMES" />
                <RowConstraints prefHeight="100.0" vgrow="SOMETIMES" />
                <RowConstraints prefHeight="100.0" vgrow="SOMETIMES" />
                <RowConstraints prefHeight="100.0" vgrow="SOMETIMES" />
                <RowConstraints prefHeight="100.0" vgrow="SOMETIMES" />
                <RowConstraints prefHeight="100.0" vgrow="SOMETIMES" />
                <RowConstraints prefHeight="100.0" vgrow="SOMETIMES" />
            </rowConstraints>
            <Button fx:id="startButton" onAction="#start">start</Button>
        </GridPane>
    </children>
</VBox>