The singers are among the stars taking part in Time magazine's annual Letters From Dad series, and in Martin's heartfelt note to twin sons Matteo and Valentino, he reveals being their dad is a real dream come true and he credits the boys with changing his life for the better.

Martin, who 'came out' as a gay man in 2010, writes, "Above all, my beautiful sons, your love gave me the strength to live an honest life. A life of courage and transparency, which fills me with great pride and peace. What an amazing gift you have given me, and I'm forever thankful to you."

He adds, "If there is anything I want you to live with, aside from knowing that you are unconditionally loved and adored by me and our family and friends, it is that you can be YOURSELF. Don't ever let anyone or anything make you feel like you can't be your true self."

Meanwhile, rocker Juanes has opened his heart to his kids Luna, Paloma and Dante, with his model/actress wife Karen Martinez, describing the moment they came into the couple's lives.

He writes, "I would feel a mixture of joy and nerves come over me that I could not describe with words alone. And then, in the blink of an eye, as when a candle is lit in the darkness, you would appear, illuminating the whole place."

Precious director Lee Daniels, who has been open about his troubled relationship with his late father, also shared his letter to his kids Clara and Liam, writing, "My dad didn't know how to tell me he loved me. I know that he did, in his way. But he never told me. And what I've learned from him, God rest his soul, is how important it is to tell you both how much I love you, every day, even when I'm angry."

Rocker Pete Wentz, actor Hank Azaria and hip-hop mogul Russell Simmons are also featured as part of the Letters From Dad series.