Dark Angel stars Alun Armstrong and Jonas Armstrong have admitted they often get mistaken for father and son.
The veteran actor does actually have a son in the trade called Joe Armstrong, and to make things even more confusing, Joe and Jonas have previously worked together.
Explaining how baffling that many Armstrongs in one room are, Jonas said of the common mistake: "It happens a lot. I'm friends with Alun's son because he was also on Robin Hood.
"There have been times on jobs where lads on the crew have come up to me and said, 'Oh, I was working with your dad the other month'. I'm like, 'Oh, yeah. What was that?' Not realising until later they mean Alun Armstrong. My dad is a trader. He does events like the Ideal Home Exhibition at the NEC and things like that.
"I'll then tell Alun's son Joe and we'll have a laugh about it. When I was cast in Dark Angel, with Alun again, I sent his son a text and said, 'It's going to confuse you even more'."
And just to add to the tangle, Jonas plays a character called Joe in the ITV period drama about a serial poisoner, played by Joanne Froggatt.
Alun added: "With names like that they do get mixed up. They worked together in Robin Hood. A lot of people think Jonas is my son."
The star recently turned 70, but reckoned he had never expected to be marking the milestone birthday.
He said: "I had a little party at my house with a few friends. But as I said to them all, 'I've left it to the last minute because I didn't really believe wholeheartedly I'd actually make it to the milestone'.
"People have been telling me all my life, 'If you carry on like this you'll be lucky to see 50´. Then 60 and 70. I always burned the candle at both ends. But I've made it. So far."
:: Dark Angel airs on ITV this autumn.