Celebrity birthdays: Kourtney Kardashain, Melissa Joan Hart and Conan O'Brien turn one year older

Kourtney Kardashian, Melissa Joan Hart and Conan O'Brien are among the many stars who are celebrating turning one year older on April 18.

Kardashian turns 40, while Hart turns 43 and O'Brien rings in 56.

The eldest of the Kardashian-Jenner clan is celebrating the big 4-0 on Thursday and recently proved age is but a number when she posed in nothing but her birthday suit.

She captioned the sexy snap: "Love yourself as deeply as you love them."

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As for Hart, the "Sabrina the Teenage Witch" star recently made headlines when she spoke about the college cheating scandal, commenting that actresses Felicity Huffman and Lori Loughlin maybe "didn't understand" that they were breaking the law.

And as for the late-night host? O'Brien has been busy with his TBS show and making political jabs at President Trump.

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Here is a list of other stars celebrating their birthdays today:

Actor Robert Hooks is 82. Actress Hayley Mills is 73. Actor James Woods is 72. Actress Cindy Pickett ("Ferris Bueller's Day Off") is 72. Keyboardist Walt Richmond of The Tractors is 72. Bassist Jim Scholten of Sawyer Brown is 67. Actor Rick Moranis is 66. Actor Eric Roberts is 63. Actress Melody Thomas Scott ("Young and the Restless") is 63. Actor John James ("Dynasty," ''The Colbys") is 63. Bassist Les Pattinson of Echo and the Bunnymen is 61. Actress Jane Leeves ("Hot In Cleveland," ''Fraiser") is 58. Ventriloquist Jeff Dunham is 57. . Actor Eric McCormack ("Will and Grace") is 56. Actress Maria Bello is 52. Actress Mary Birdsong ("Reno 911!") is 51. Actor David Hewlett ("Stargate: SG-1") is 51. Actress Fedro Starr ("Moesha") is 48. Actor David Tennant ("Harry Potter and the Goblet of Fire") is 48. Guitarist Mark Tremonti of Creed and of Alter Bridge is 45. Singer Trina of Trina and Tamara is 45. Actor Bryce Johnson ("Pretty Little Liars") is 42. Actress America Ferrera ("Ugly Betty") is 35. Actor Tom Hughes ("Victoria") is 34. Actress Ellen Woglom ("Marvel's Inhumans") is 32. Actress Vanessa Kirby ("The Crown") is 31. Actress Alia Shawkat ("Arrested Development") is 30. Actress Britt Robertson ("Under the Dome") is 29. Actress Chloe Bennet ("Marvel's Agents of S.H.I.E.L.D.," ''Nashville") is 27. Singer Nathan Sykes of The Wanted is 26. Actor Moises Arias ("Hannah Montana") is 25.