Alex Grayle

 was a boy that Charley Pollard met in England in 1930. Sparking her sense of adventure, Alex agreed to meet with Charley in Singapore on New Year's Eve. Charley subsequently stowed away on the R101 as the first leg of her journey there, ran into the Eighth Doctor en route, and became his companion. (BFA: Storm Warning)

Alex's first Singapore rendezvous was in a divergent timeline set up by Alex's grandfather Sebastian Grayle. That timeline was created specifically so that Sebastian could gloat over having killed the Doctor in a previous encounter. With the resolution of the paradox surrounding Sebastian, this meeting (and timeline) ceased to exist. (BFA: Seasons of Fear)

Charley and the Doctor subsequently met up with Alex at the Raffles Hotel in Singapore in the mainstream timeline, as planned. (BFA: Seasons of Fear)