The pair struggled to reach the UK for a scheduled appearance on The Graham Norton Show on Thursday after becoming stuck in Berlin by the ash cloud spewing from the island country's most active volcano, which has sparked widespread flight delays and cancellations.
They had been in Germany for the comedy sequel's European premiere on Wednesday.
Recalling their journey on Norton's BBC One programme, Cooper exclaimed: "We were in Berlin today. We just got here."
Helms added: "We've been on a mad dash, fighting the volcano. I cannot be beaten. Clearly Mother Nature did not want us here."
The Hangover: Part II, which also stars Zach Galifianakis and Justin Bartha, is currently playing in UK and US cinemas.
> Watch our interview with Bradley Cooper and Ed Helms
Watch the trailer for The Hangover: Part II below: