For Gwen Stefani, 40 truly is the new 20. The 'Hollaback Girl' singer and fashion icon is looking as beautiful as ever on the cover of Elle UK's April 2011 issue, which hit stands yesterday. Stefani portrayed the ultimate 'Blond Bombshell,' Jean Harlow, in the 2004 biopic 'The Aviator,' and she seems to be channeling the same retro look in her Elle spread.

Stefani was also interviewed by friend and fellow singer Shirley Manson, and she opened up about her workout-beauty regimen and designing for her fashion line, L.A.M.B.

When it comes to working out, Stefani is extremely dedicated to staying in shape. "I work out five days a week, I can't imagine not doing it," she tells Elle UK. "I'd like to have no rules and eat what I want, but I've learned over the years that I'm so disappointed when I can't wear the clothes I want to wear."

Working out is not an option for Stefani, but a lifestyle, especially because the singer-designer is her own worst critic. "And if I let myself down, appear on stage when I'm not looking my best, it's not fun for me," she adds. "I just beat myself up about it."

Stefani also keeps herself looking and feeling her best by sticking to her daily routine of applying makeup. She says, "I wear make-up every single day; I like to wear make-up for Gavin and I don't feel energized till I've put it on, then I'm ready to go."

Although her successful fashion brand, L.A.M.B., came into being in 2004, Stefani continues to find motivation by being critical of herself. "I'm not even close to being where I want it to be yet," she shares with Elle UK. "[Fashion] is very, very hard to do well, but I'm learning. I'm getting to the point where the last collection we did was a disaster until two weeks before -- I had to fly to Montreal and review the whole collection -- and it ended up being one of the most cohesive collections we'd ever done."

In other news, Stefani will be donating her Dior wedding gown, which she wore during her 2002 wedding to English rocker Gavin Rossdale, to the Victoria and Albert Museum in London. "I didn’t wanna send it because I was scared it would get ruined. But it’s a work of art, it needed to be seen." The dress, which Stefani calls her "favorite outfit," is the brainchild of ex-Dior designer John Galliano, who was let go after making harsh anti-Semetic remarks at the end of February.

Stefani is currently working on an upcoming No Doubt album. She also recently showed off her latest batch of L.A.M.B. looks at Fashion Week in NYC in February.

Watch the Behind-the-Scenes Video of Gwen Stefani's Photo Shoot for Elle UK

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