Elizabeth line Stratford to Farringdon, then circle, Metropolitan, or Hammersmith and City line or bus 63
South-Eastern high speed service from Stratford International to St.Pancras in about 7 minutes (Note that Stratford International is a separate station, not accessible except by means of a short bus or DLR link from the main station)
London Overground Train Stratford to Caledonian Road and Barnsbury, then 10 minute walk or any bus to King's Cross.