This is awkward. I don't know how to put this and I don't know what to say because noone will possibility believe me. But I'm facing eviction from the home that I live in as soon as I show my face. Something weird has happened.

I started glowing, all around my body and within a minute, I had changed. Literally and physically changed. I'm the same and yet a completely different person. I was completely alone so I had no witnesses.

How do I convince my family that I'm still me, despite having no way to prove my identity that. I'm now looking completely different to my driving license photo

I don't know what to do!!!!

Do you have any psychic paper?

No, I don't know what that is?

Oh well.. play time's up.

I smell a Melody Pond sitcom!

Despite the humourous nature in which this thread was started I think it raises a point nevertheless. Mostly we see the doctor regenerate in front of a companion, or meet new companions who have never known him any different or if he sees someone who knew him in his old form who hasn't seem him regenerate he just tells them he's the doctor and they believe him. What if they didn't though?. What if he tried to tell them he was the doctor and they didn't believe it, or maybe even saw something that made them think otherwise, how could he convince them beyond doubt?

I think a good example of what Im thinking is the Eccleston to Tennant regeneration and subsequent children in need minisode. Despite the doctor having to convince rose in the minisode he was still him, she didn't take much convincing because she'd actually seen it happen as he pointed out, but say she hadn't seen the change, and had maybe woken up after the change, she would see this new man in the tardis, who in that minisode seemed crazy and maybe a little menacing, so even though he would still say he was the doctor, she probably would have took much longer to convince. Even when he described things they'd done together, without being in the frame of mind where she'd actually seen the change she could easily have thought it he was an imposter who had being spying on them.

Similarly, had Clara got back to the TARDIS after the change in time of the doctor to find an older man who didn't know how to fly the TARDIS and was ranting about his kidneys, she may have been inclined to not believe him saying he was the doctor, again he'd have to find some way to convince her.

Basically, how does a new doctor convince an old friend beyond doubt that he is him? (and don't say DNA test because he'd have to have DNA the friend knew beyond doubt was from the old body to compare with his DNA and I doubt that would be likely)

What was it that convinced the Brigadier? Or did he just pragmatically decide that he didn't have time to worry about it?

Stethoscope? That would rule out anyone who wasn't a Time Lord.

That would be an interesting scenario. Never been tried that way.

The Doctor recognised him. From the medical description and presence of the TARDIS the Brigadier was sure it would be the Doctor, but upon seeing him he said it was the wrong man. Then the Doctor muttered 'Lethbridge-Stewart'.

That would prove him a timelord, Given but as we see by the way the master keeps coming back and how in the doctors wife he really thought there might be living timelords in the bubble universe that despite most not being around, even the doctor isn't sure whether other timelords might pop up any time, so if a companion was so difficult to convince because the new incarnation was acting so strange beacuse of the post regeneration trauma, or the new incarnation appeared to not know things the companion knew the doctor does know, like Capaldi not knowing how to fly the TARDIS, then they could just think it was an imposter timelord, or even some sort of trickery with the stethoscope

I think it would have to be something personal to convince them, but something that was more than just information about their travels which someone could acquire, that would leave no doubt. I this would be an interesting scenario to explore in an episode. The only convincing way I can think of they could resolve it would be to maybe show the outgoing doctor interacting with the TARDIS in some way where it only happens that way for him, then doing that thing again as the new doctor is what convinces them.

Made me chuckle that did.

I believe that Time Lords can "sense" each other. I think Ten mentioned something about it in The Sound of Drums that The Master had used Archangel to block their link.

In Utopia, when Yana opened the watch and became The Master, Ten knew an instant what had happened, and that knowing look Ten gave The Master when they met eyes for the first time. Time Lords just know!

Was talking about non Timelord friend/companions.

OOps!

Well then perhaps if his compansions and friends meet him in a future incarnation they'll be able to guess on intuition. like Sarah Jane in School Ruinion. (Yes she did have the TARDIS for a big clue) .

Perhaps, and indeed your right that's often the case, but was wondering how, if they didn't intuitively know and didn't believe he was who he said he was, there was some way, more than just giving info (which could be found out by anyone), he could actually completely prove his identity beyond doubt.

is it in 3 doctors - or 5 doctors - that The Brig takes no2 as the real one ? for no 3 he hides the key to the tardis.......

the dr usually regenerates with other people present so they know its him ...... and the tardis knows and he can operate it

... but Ben didn't believe Troughton was the Doctor even though he saw it, right?