The Doctor and Amy Pond go back to Van Gogh's time to figure out why there is an alien in one of his paintings. Things happen, the mystery is solved and the alien is vanquished. But because Vincent is still depressed, they take him forward in time to see an exhibit of his works in Paris in the 20th (or 21st?) century. Vincent gets to see that he will not be viewed as a failure, that his art is revered.
But when the Doctor and Amy leave Vincent in 1890 and return to the future, nothing has changed. Vincent still committed suicide mere weeks after their encounter. Though they brought some good into his life, it wasn't enough to overcome the bad (and sad).
I sobbed the first time I saw this, and it still gets me in the feels every time. For Vincent to feel such a failure, and then to find out that his life and his work had meaning to the rest of the world... I ended up reading (and viewing) all that I could find about Van Gogh. In particular, there was a TV documentary called Painted With Words (2010), with Benedict Cumberbatch, that portrayed the relationship between Vincent and Theo. I now have Van Gogh works as the home screen and lock screen on my phone (Starry Night and Wheat Fields with Reapers, respectively). I have become a serious fan of Vincent Van Gogh, simply from watching a simple, kids' science fiction show.