Dannii Minogue admits it is a "great sadness" that she has a child and her sister Kylie doesn't.
The 45-year-old singer - who has six-year-old son Ethan with ex-boyfriend Kris Smith - has never been as maternal as her famous older sibling, and was always in awe of how the Wow hitmaker instinctively knew how to interact with their nephew Charles, now 10, and she didn't.
Though Dannii never had a strong desire to have kids of her own when she was younger, seeing Kylie - who is engaged to actor Joshua Sasse - deal with her heartbreak at not having a family has made her appreciate just how "blessed" she is.
She said: "Growing up, it was Kylie who always wanted kids and I never really did. When my brother Brendan had his little boy, I hadn't a clue even how to hold him. I remember being really impressed by Kylie because she just instinctively knew what to do.
"When he was a bit older, she'd be the one rolling on the floor with him, making him laugh his head off and I'd be thinking, 'What do I do?' When I got pregnant I was completely shocked.
"But having a baby changed everything. Kylie has been incredible with Ethan. She just loves him - I love to see them together.
"[Not having her own kids is] a great sadness for her, it's a great sadness for me and it's also made me really understand how blessed I was to be a mother.
"When I got pregnant, I was completely shocked - but having a baby changed everything.
"Kylie wrote a song called Flower about how she feels about motherhood. It's so beautiful it makes me cry. But you just don't know what is going to happen in life."
Dannii is now in a relationship with producer Adrian Newman and though she and 48-year-old Kylie - who previously battled breast cancer - have been through tough times in the past, things are good now and they know they can always rely on one another for support.
She told Stella magazine: "I'm genuinely happy now.
"I'm dog-tired because I'm a single mother and no one warns you how tiring having a super-active little boy is. But life is good. And it's the same for my sister...
"Life hasn't been smooth sailing for either of us. We've had some incredibly lucky, wonderful times and we've had a lot of dark days. But I don't think there's a woman out there who hasn't experienced both in her life.
"All I do know is I have a sister - and a family - who I love very dearly. If there's something wrong with my sister, I can't even sleep at night and it's the same with her about me. Our family has always been very close."