As Inspector Sam Tyler in Life On Mars, John Simm collapsed after waking up in the 1970s.
But the actor now faces his own life-changing puzzle: he must discover that the man he idolized and thought was his biological father was actually not.
The revelation came after Simm, 54, took a genetic test for ITV’s DNA Journey.
Ironically, he only appeared on the show to support his friend and fellow Life On Mars co-star Philip Glenister, 61, who played the brash and politically incorrect DCI Gene Hunt.
The two men met 17 years ago when they became the actors behind the police duo – and Simm said he took part in the show alone, so Glenister wasn’t on his own.
Phil Glenister (left) and John Simm (right) on ITV’s DNA Journey, which airs on October 9
John Simm also discovers he has a half-sister Karen who he meets on ITV’s DNA Journey
John Simm’s real biological father Terry Smith is depicted, as part of the DNA Journey episode
Simm said: ‘It’s become such a big thing in my life and all I did was a favor for Phil so he didn’t have to do it alone. It made my world spin, and everything I thought I knew wasn’t real.”
Leeds-born Simm started in the entertainment world as a young teenager, playing guitar in a band alongside his musical father Ronald.
Ronald died in 2015 and about his grief, Simm once said in an interview: ‘When someone dies, you are left with a huge black hole in your life.
“People say, ‘You’ll get over it,’ but I don’t want to get over it. I always want to remember my father. I still have his number in my phone.
“Every now and then I see something on TV that I think he would like and I pick up my phone to text him, I still do.”
In the fifth season of DNA Journey, he recalls a conversation he had with his mother before taking the test for the program.
He said: ‘When they had me, in the Sixties, they were both young. They were together and then they broke up and were both with other people and then they got back together and then they had me. And I had never heard this story before.”
John Simm (left) appeared on the show in support of Life On Mars co-star Philip Glenister (right)
John Simm (left) took a genetic test with co-star Philip Glenister for ITV’s DNA Journey
Philip Glenister (left) and John Simm (right) are friends and co-stars of Life On Mars
After the DNA reveal, Simm considered withdrawing from the program, but decided to call in the show’s experts to find out more about his biological father.
During the episode, he is told that his biological father has died, but discovers that he lived in the same area as Simm and would drink at the same working-class clubs that he and his father played in.
“What blows my mind, my dad and I, we’ve played here a lot, we’ve certainly played here a lot and he could have been in the same pub one night and seen me play,” he said.
“I can’t get it out of my head because we played in this area in the 80s and he was here and worked in gentlemen’s clubs. It’s one of those crazy Back To The Future, Life On Mars things.’
Dad-of-two Simm also discovers he has a half-sister Karen who he meets at the end of the episode and who shares memories with him about their biological father.
John Simm (left) and Phil Glenister (right) will appear in a new episode of ITV’s DNA Journey
Philip Glenister played DCI Gene Hunt and John Simm played DI Sam Tyler in Life On Mars
John Simm and his wife Kate Magowan at an English National Ballet party in London in 2013
In addition to Life On Mars, Simm starred alongside Dougray Scott in the TV adaptation of author Irvine Welsh’s novel Crime.
The ITV drama followed the exploits of troubled Edinburgh detective Ray Lennox, played by Scott.
Filmed in Edinburgh and Glasgow, the first series aired in November 2021.
Simm played Gareth Horsborough, also known as Mr Confectioner, who was the main antagonist in both series.
The new episodes of DNA Journey will also star Ricky Tomlinson and Sue Johnston and James Nesbitt and Sarah Parish.
John Simm and Philip Glenister’s DNA Journey with Ancestry airs on Wednesday October 9 at 9pm on ITV1, ITVX, STV and STV Player