Aguilera 'Thrilled' For Spears

Christina Aguilera is overjoyed after learning her chart rival Britney Spears has become a mother.

Lady Marmalade singer Aguilera admits her former The Mickey Mouse Club co-star's pregnancy hadn't really registered until she gave birth to Sean Preston on Wednesday.

She tells Mtv News, "My assistant came in the room when it happened and she's like, 'Britney had a boy!' and I was like, 'Oh my gosh!'

"I don't know where I was for a while when she was pregnant but it really kicked in at that point. It's like, 'Wow, she had a baby! That's crazy!'

"I'm overjoyed and thrilled for her. It's such an exciting time in her life and I just wish her the best."

Aguilera says she has already sent Spears a baby gift and a card.