The Queen has tweeted her thanks for the well wishes on her 90th birthday, from the official Twitter account of the Royal Family.
I am most grateful for the many digital messages of goodwill I have received and would like to thank you all for your kindness. Elizabeth R.— The Royal Family (@RoyalFamily) June 21, 2016
And there's a picture, too! It's almost as though they think we won't believe it was really her... (True.)