It all started with this tweet from Jedi News UK:
Something fun. Go on Google maps. Type in LONGCROSS studios. Zoom in. See what you can find... satellite view ne… https://t.co/VALJNNNH4J pic.twitter.com/Eae7n3Mfw5— Jedi News (@JediNewsUK) June 16, 2017
That led to an online scavenger hunt of sorts, with fans coming across the image you see above.
Ha found the Falcon thanks for the heads up pretty cool pic.twitter.com/TAGCO10e97— Woodrow Hull (@woodysalaskan) June 17, 2017
Last year, StormtrooperLarry.com reported that filming for The Last Jedi at Longcross included the Falcon, so this is obviously the same ship, hidden for safe keeping.