Sheridan Smith said she was too "star-struck" to take up Cilla Black's offer of a friendly chat for advice on playing her on-screen.
The actress received high praise for her starring role in ITV's drama series Cilla in 2014 b ut admitted she was overwhelmed when meeting the entertainer, who died a year later at the age of 72.
However, Smith has managed to forge a friendship with another person she is depicting on the small screen; Julie Bushby, the mum who led the community search for nine-year-old Shannon Matthews in 2008.
The 35-year-old said she loved to get "lost" in real-life characters and cited both Black and train robber Ronnie Biggs's wife Charmian - whom she portrayed in 2012 TV series Mrs Biggs - as those who left the greatest mark.
Speaking to Radio Times, Smith said: "I love getting lost in the characters I play and when that character is a real person there is lots of background and research I can delve into.
"Meeting Charmian Biggs and Cilla Black was fascinating and I spent hours talking to them, watching videos of them and reading books about them.
"I did get a bit tongue-tied meeting Cilla and I was too star-struck to take up her offer of ringing her any time if there was anything extra I wanted to ask her but I fell in love with both of them - as I did with Julie.
"I felt such a bond with them."
Smith now counts Ms Bushby as one of her friends after spending time with her during the filming of the BBC's The Moorside, which recounts the Shannon Matthews case.
Karen Matthews became notorious after her daughter, Shannon, disappeared from their home in Dewsbury, West Yorkshire, only to turn up 24 days later, hidden in her stepfather's uncle's home, less than a mile away.
Matthews and Michael Donovan were jailed after a court heard that they planned the disappearance in an attempt to claim a cash reward.
Smith said she has become close with Ms Bushby after spending time with her on the Moorside estate during filming last year.
She said: "I am still friends with Julie. She's a great mum and grandmother and, although she doesn't always let it show, she has a heart of gold.
"There was a really emotional scene I had to play where my character talks about losing her baby boy to cot death. She stayed up all night with me discussing what had happened and how she had coped, just to help me play the scene."
Smith said Ms Bushby helped her with her fears over her sick father, who died just before Christmas.
She said: "At the time I was so worried about my dad, but I learnt a lot from her that night about staying strong for those you love and for that I'll always be grateful."
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