Image gone after GestureRecognizer tap

Hello, so I'm working on an an app that should basically display a picture after you tap it. Like a photo viewing app.

The problem I have is that when I press one of the images in a grid, the app does what it should, but when I return from the tapGestureRecognizer method, the Image preview in the grid is gone. I wanted to post screenshots but apparently I'm too new a user to be allowed something dangerous as that.
I don't know what I'm doing wrong, it's probably something simple but I can't get my head around it.

Thanks for help!

Code (not working in XAML):

using Android.Widget;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;

namespace App7
{
    public partial class MainPage : ContentPage
    {
        private Grid firstGrid;
        private bool fullScreenOn = false;
        private ContentView mainContentView;

        public MainPage()
        {
            InitializeComponent();

            // AppHandler test = new AppHandler();

            mainContentView = new ContentView();

            firstGrid = new Grid();

            firstGrid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) });
            firstGrid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) });
            firstGrid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) });

            // making a square 2x3 grid
            firstGrid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });
            firstGrid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });

            // when clicking an image, this ContentView will fill the entire screen
            ContentView fullscreenView = new ContentView();
            fullscreenView.BackgroundColor = Color.Black;
            fullscreenView.HorizontalOptions = LayoutOptions.FillAndExpand;
            fullscreenView.VerticalOptions = LayoutOptions.FillAndExpand;
            //mainStackLaout.Children.Add(fullscreenView);
            //mainStackLaout.LowerChild(fullscreenView);

            var tapGestureRecognizer = new TapGestureRecognizer();
            tapGestureRecognizer.Tapped += (sender, eventArgs) => {
                fullScreenOn = true;
                Image fullScreenImage = (Image)sender;
                fullscreenView.Content = fullScreenImage;
                mainContentView.Content = fullscreenView;
            };

            Image image1 = new Image() { Source = "aniso.jpg" };
            image1.GestureRecognizers.Add(tapGestureRecognizer);
            Image image2 = new Image() { Source = "band.png" };
            Image image3 = new Image() { Source = "basophil.png" };
            Image image4 = new Image() { Source = "basophil2.png" };
            Image image5 = new Image() { Source = "bild5.jpeg" };
            Image image6 = new Image() { Source = "blast.jpg" };

            firstGrid.Children.Add(image1, 0, 0);
            firstGrid.Children.Add(image2, 1, 0);
            firstGrid.Children.Add(image3, 2, 0);
            firstGrid.Children.Add(image4, 0, 1);
            firstGrid.Children.Add(image5, 1, 1);
            firstGrid.Children.Add(image6, 2, 1);

            mainContentView.Content = firstGrid;

            Content = mainContentView;
        }

        protected override bool OnBackButtonPressed()
        {
            if (fullScreenOn)
            {
                mainContentView.Content = firstGrid;
                fullScreenOn = false;
                return true;
            }
            return base.OnBackButtonPressed();
        }


    }
}