In March's Doctor Strange #12, the titular doc will become the herald of Galactus. In April's Doctor Strange #13…he might become Galactus himself? That's what we call a promotion!
Marvel teased the issue, which will be solicited soon, on their website:
Last month, Marvel.com teased the new role of Doctor Stephen Strange as the Herald of Galactus in DOCTOR STRANGE #12 (on sale Wednesday, March 6). Writer Mark Waid said that Strange was "[o]utpowered and out of his element," and now tasked with "[preventing] the World-Eater from destroying the entire magic cosmos!" But now, in DOCTOR STRANGE #13, Galactus has been set loose on other dimensions and devouring those worlds — which could have cosmically dire consequences! It's up to Strange to prevent an interdimensional disaster. No pressure!
Mark Waid writes Doctor Strange #13 tortiously (that means like a tortoise) with art by Barry Kitson and a cover from Jesus Saiz: