What was the relationship between Sher Khan and Humayun?

After his defeat in the Battle of Ghagra in 1529, Mahmood Lodi wanted to try his luck once again in 1530. He felt that time was opportune for a trial of strength. Humayun was seriously ill and later on when his life was saved, Babur died. Soon after his succession to the throne, the hands of Humayun were full an consequently he could not be expected to deal effectively with the affairs of a distant place like Bihar. Mahmood Lodhi got the help of all the Afghan Chiefs. He had to take special pains to enlist the support of Sher Khan.

Many months were spent in preparations and the Afghans occupied the territory up to Banaras. When they marched towards Jaunpur, Humayun got upset. At that time, he was busy with his siege of Kalinjar. He hastily made peace with the Raja of that place and advanced against the Afghans. In the Battle of Dourah in U.P. in August, 1532, the Afghans were defeated and Mahmood Lodi ran away. Sher Khan was throughout an unwilling worker and soon after the failure of the Afghan attempt, he recovered South Bihar.

After his success against the Afghans, Humayun besieged the Fort of Chunar which belonged to Sher Khan. “The Fort of Chunar stands on a rock close to the Ganges, and is, as it were, a detached portion of the Vindhya Mountains which extend to the same river near Mirzapur. From that neighbourhood the hills recede westwards, by the Fort of Rohtas and Shirghari, and do not approach the river again, until near Bhagalpur, after which they run straight South, leaving the Ganges at a great distance.

These hills, therefore, covered the whole of the South-West of Bihar and Bengal, and shut up the road along the south bank of the Ganges, in two places-one near Chunar and the other at Sicragalli, East of Bhagalpur. The hills themselves are not high, but poor and covered with woods. The siege lasted for 4 months and during all this period Sher Khan was able to defy the might of Humayun.

However, Humayun made peace with Sher Khan as he got news of trouble in Gujarat by Bahadur Shah. Sher Khan was allowed to continue in possession of Chunar on the condition that he was to send a contingent of 500 troops for service in the Mughal Army. These terms were accepted by both the parties in January 1533.