Georgia welcomed her son Ty in 2002 aged 17 following a brief relationship. David adopted Ty in 2011, the same year as he married Merlin and The Bill star Georgia.
Below, we look at David and Ty's close relationship…
When David Tennant met Ty
Ty has previously spoken of the moment he met dad David on the set of Doctor Who, when he was aged five.
David met Ty's mum Georgia when she had a guest role in the 2008 episode The Doctor's Daughter - and it was then that Ty met his TV hero.
"It was great, I was five when I first met my dad, my mum was working on Doctor Who at the time," Ty said. "I watched him on TV as the hero, and it was crazy how much your life can change."
David Tennant on being a father
In an interview with Candid magazine, David revealed: "Our kids are lovely, and I think that being a dad is one of the most extraordinary and life-affirming things that can ever happen to you, as well as being something you have to keep working at if you're going to be any good at it."
David also addressed the reason why he and Georgia have decided not to talk about their children in interviews.
The doting dad explained: "But the kids don't ask to be photographed when we're walking down the street, and we've decided that if we don't talk much about them in public, then we can maintain a bit of moral high ground to be able to say to photographers, 'Look, we don't talk about them, so you don't need to take their picture'".
David Tennant on Ty's acting
Like his parents, Ty is making his name as a successful actor and has already starred in House of the Dragon, Tolkien, Doom Patrol and War of the Worlds.
David has talked in the past that he was worried Ty would be "rubbish" at acting, telling Candid magazine that he was delighted to discover he was actually "incredibly talented".
We wonder if he'll take on his dad's Doctor Who role in the future like his dad David? Ty's maternal grandfather Peter Davison also played the Doctor! He was the fifth Doctor in 1963, so it clearly runs in the family.
In 2020, Ty The Sun: "Doctor Who is such a massive thing to take on. I don't think I would ever decline the offer."
He added: "Whoever is truly right for it will get the role. If I am granted that, I will certainly do my best."
Ty Tennant on his parents having a fifth baby
David has previously joked that Ty gave his parents a telling-off after they told him that they were expecting their fifth child.
Chatting on The Graham Norton Show, he said: "We have number five child on the way. It's very exciting. There is a big spread of ages, with a 17-year-old at one end. When he found out about the new baby, he was like, 'You're having another one?' It's odd when a 17-year-old is giving his parents a lecture on birth control!"