Taron Ergerton has assured fans that he is “completely fine” after collapsing on stage during the opening night of his new West End play.

Theatre goers were left concerned after the Welsh actor, 32, was taken ill during the production of Cock at the Ambassadors Theatre in London on Saturday night.

Thankfully, a doctor was in the house and attended to him as the show took a 40-minute break.

While director Marianne Elliot appeared on stage to reassure that the actor was “fine”, his understudy, Joel Harper-Jackson, filled in for the remainder of the performance as a precaution.

Taking to Instagram Stories the following day, Egerton, who is best known for playing Elton John in musical biopic Rocketman, gave his 2.5m a health update.

“As some of you may have heard, I passed out during the first performance of Cock last night,” he wrote. “I am completely fine. Slightly sore neck and a bruised ego but I’m fine.”

“I’ve decided to put a positive spin on it and I would appreciate it if anyone who was in the theatre last night just said that I gave such a committed, electrifying performance that my body couldn’t handle it and checked out,” he jokingly continued.

“That being said, apparently you’re meant to do the full show and not just three quarters of it. So I’ll be back with a vengeance tomorrow night.”

He went on to thank his “amazing” castmates and members of the production team, as well as Harper-Jackson.

A statement from the play addressing the issue read: “During this evening’s first preview of Mike Bartlett’s play Cock at the Ambassadors Theatre, Taron Egerton fainted towards the end of the performance.

“A doctor who was in the audience attended to Taron immediately after the incident, and whilst he felt fine, it was decided that Taron’s understudy, Joel Harper-Jackson would continue in the role to complete the performance”

Cock marks Egerton’s West End debut and follows a gay couple who are rocked when one of them falls in love with a woman.

The play is written by Mike Bartlett and also stars Jonathan Bailey, Jade Anouka and Phil Daniels.