Where Liv Tyler and adoptive father Todd Rundgren stand after realizing Steven Tyler was her biological dad at a concert

Liv Tyler has opened up about the 'beautiful way' she discovered she has a sister and her biological father is Steven Tyler, but how 'hard' it's been on her adoptive dad.

The Lord of the Rings star grew up with her mom, singer and former Playboy Playmate Bebe Buell and adoptive dad, rock musician Todd Rundgren.

However, when she went to an Aerosmith gig aged around '11 or 12', she ended up bumping into Mia Tyler - Steven's daughter with his first wife Cyrinda Fox - while Guns n' Roses were singing 'Welcome to the Jungle'.

Liv noticed a girl at the side of the stage realizing it was like 'looking in a mirror seeing double' and her mom then burst into tears, revealing they actually shared a dad - Aerosmith frontman Steven Tyler.

But what did this mean for Liv's relationship with her adoptive dad?

Liv Tyler was brought up by adoptive dad Todd Rundgren (Dimitrios Kambouris/Getty Images)

During an appearance on an episode of iHeart radio podcast, Sibling Revelry With Kate Hudson and Oliver Hudson - which aired on April 13 - Liv explained Steven was battling with drug use at the time her mom was pregnant with her.

The 47-year-old continued: "As the story goes, [my mom] called Todd and said she was pregnant and he asked her to come home to where they lived in Woodstock in upstate New York.

"He very courageously and lovingly said, ‘This child needs a father and I will be the father'."

Liv was subsequently born 'Liv Rundgren,' adding in an interview with AP in 2001: "'I don't think my dad was in any position to be a father. Steven, that is. What an amazing thing Todd did for me."

When she found out who her biological dad was after the concert, Liv reflected the 'first wave' of emotions was 'shock'.

Liv Tyler with biological parents Bebe Buell and Steven Tyler (Jeff Kravitz/FilmMagic, Inc/ Getty Images)

However, she added: "I remember sitting there for what felt like three days, but it was probably three hours, and coming to this conclusion of ‘Whoa, I have two dads and all this love'."

Ultimately, the actor noted she was 'just really excited about' having two days 'because they're all so different and so lovely'.

She resolved: "I love him. I have brothers from him and I had a whole family with them. He took care of me like he was [my] dad."

However, she acknowledges 'it's probably still very hard and painful,' for Todd and she added that she 'do[esn't] speak to him enough'.