David Oyelowo admitted it is "impossible" to find the perfect Christmas gift for Oprah Winfrey.
The 43-year-old actor - who has four children with wife Jessica - is very close to his 'Butler' co-star and has learned the media mogul appreciates a "really well-written" letter more than any material gift.
Speaking about having spent Christmas with Oprah and what to buy her as a gift, he said: "It's impossible. The thing she really does love is words. If you write something from the heart that really moves her. She's a godmother to [my kids].
"A really well-written letter is the thing that does it for her."
The 'Wrinkle in Time' actor also explained he has a special nickname for Oprah, Mummo, because of the kindness she has shown his family.
Speaking on 'The Jonathan Ross Show' in an interview airing on Tuesday (24.12.19) on ITV, he said: "The reason I call her Mummo, this to me is what the heart of this season is and what she represents.
"My mum had a brain aneurysm about four years ago and she ended up passing from it. Oprah knew about this and she knew how much my mum meant to me.
"My mum was in hospital with my dad here in London. I was on set, I suddenly got a call from Oprah, she said, 'I'm in London, I was on my way to South Africa, and I know your mum is here, right? I want to go and see her'.
"I told her where my mum was, she went, then called me again from the hospital lobby. I called my dad, 'Oprah is coming to see mummy, get in the hospital now'. He was stuck in traffic. She was sat in the hospital lobby on her own.
"She called me and said, 'Where's your dad?'. I said, 'He's on his way, but he's stuck in traffic'. She said, 'OK hold on David, just another selfie...' literally while I was on the phone to her, she was getting more and more [people coming up to her]. She said, 'I think I'm going to have to find somewhere to be.'
"She waited for my dad for an hour and a half and then spent two hours with my mum... That's why she's my Mummo."