Madame Vastra says to Clara that the Doctor trusted her when he regenerated and became an older man, showing his great age and "lifting the veil", the Ninth Doctor regenerates to become even younger than before. Does this mean that the Doctor didn't trust Rose like he trusted Clara, or became younger to flirt with Rose?
Well that's only Vastra's theory - and she's arrogant, so she talks like she's right. To be fair she generally is. But let's also remember that the Doctor is in a very different place in his life. Chris was the war survivor Doctor, the high-plains drifter, pushing everyone away. But he's brought back to life by a girl he falls in love with, and when he regenerates perhaps he reaches out to her a bit. He becomes a more suitable 'boyfriend'. Often when talking to women I've wished I could turn into David Tennant - and I'm pretty sure they've all wished that too.
But a thousand years on in Trenzalore is a very different learning curve. He watches generation, generation die in front of him, and remembers that he's nobody's boyfriend - he cannot afford to love or be loved. When he regenerates, instinctively, he let's Clara see who he really is.
You can read the whole article which is in DWM 479 - out now.