Goto a tabbed page from outside the tabbedpage navigation

Hi,
I have an application built with tabbedpage navigation but on some pages it's possible to open a second page trough "pushmodalasync". That new page contain a button that suppose to pop it's own page and go to a specific page in the tabbedpage hierarchy and I can't understand how I can get that to work, any ideas?
When I'm in a tabbedpage I can use the code bellow but this will of course not work when I'm in the pushed page.

    new TapGestureRecognizer()
                {
                    Command = new Command((parameter) => {
                        var page = parameter as ContentPage;
                        var parentPage = PageInfo ;
                        parentPage.CurrentPage = parentPage.Children[1];
                    })
                });

/magnus