European Space Agency astronaut Tim Peake stepped outside the International Space Station on Friday, becoming the first to walk in space wearing the British flag.

"Exhilarated -- but no time to dwell on emotions," Peake tweeted Thursday, before the big moment.

Peake, 43, was accompanied by US astronaut Tim Kopra on the extravehicular activity (EVA) to replace a failed power regulator, install a valve and attach cables outside of the station, according to the space agency.

The ESA live-tweeted the spacewalk with a blow-by-blow description of the astronaut's moving along the station's truss, unbolting the failed regulator and installing its replacement.

The spacewalk had been expected to last about six hours, but had to be cut short due to a "small amount of water" in Kopra's helmet, NASA tweeted.

Peake and Kopra were back inside the pressurized space station at 12:31 p.m. ET, NASA said.

While Peake became the first astronaut to walk in space as a British astronaut, Michael Foale -- a dual U.S. and British citizen -- was the first person born in Britain to walk in space in 1995.

Foale, however, was an astronaut for NASA, not the European program.